# multivariable chain rule second derivative

Two terms appear on the right-hand side of the formula, and $$\displaystyle f$$ is a function of two variables. Every rule and notation described from now on is the same for two variables, three variables, four variables, a… In the real world, it is very difficult to explain behavior as a function of only one variable, and economics is no different. Recall that when multiplying fractions, cancelation can be used. Calculate $$\displaystyle ∂z/∂x,\; ∂z/∂y,\; ∂x/∂u,\; ∂x/∂v,\; ∂y/∂u,$$ and $$\displaystyle ∂y/∂v$$, then use Equation \ref{chain2a} and Equation \ref{chain2b}. b. We can draw a tree diagram for each of these formulas as well as follows. Let z = z(u,v) u = x2y v = 3x+2y 1. Multivariable Differential Calculus Chapter 3. Now suppose that $$\displaystyle f$$ is a function of two variables and $$\displaystyle g$$ is a function of one variable. Have questions or comments? Featured on Meta Feature Preview: Table Support Then we take the limit as $$\displaystyle t$$ approaches $$\displaystyle t_0$$: \begin{align*} \lim_{t→t_0}\dfrac{z(t)−z(t_0)}{t−t_0} = f_x(x_0,y_0)\lim_{t→t_0} \left (\dfrac{x(t)−x(t_0)}{t−t_0} \right) \\[4pt] +f_y(x_0,y_0)\lim_{t→t_0}\left (\dfrac{y(t)−y(t_0)}{t−t_0}\right)\\[4pt] +\lim_{t→t_0}\dfrac{E(x(t),y(t))}{t−t_0}. Calculate $$\displaystyle dy/dx$$ if y is defined implicitly as a function of $$\displaystyle x$$ via the equation $$\displaystyle 3x^2−2xy+y^2+4x−6y−11=0$$. First, there is the direct second-order derivative. then substitute $$\displaystyle x(u,v)=e^u \sin v,y(u,v)=e^u\cos v,$$ and $$\displaystyle z(u,v)=e^u$$ into this equation: \[\begin{align*} \dfrac{∂w}{∂u} =(6x−2y)e^u\sin v−2xe^u\cos v+8ze^u \\[4pt] =(6e^u\sin v−2eu\cos v)e^u\sin v−2(e^u\sin v)e^u\cos v+8e^{2u} \\[4pt] =6e^{2u}\sin^2 v−4e^{2u}\sin v\cos v+8e^{2u} \\[4pt] =2e^{2u}(3\sin^2 v−2\sin v\cos v+4). Calculate $$\displaystyle ∂w/∂u$$ and $$\displaystyle ∂w/∂v$$ given the following functions: \[\begin{align*} w =f(x,y,z)=\dfrac{x+2y−4z}{2x−y+3z} \\[4pt] x =x(u,v)=e^{2u}\cos3v \\[4pt] y =y(u,v)=e^{2u}\sin 3v \\[4pt] z =z(u,v)=e^{2u}. Calculate $$\displaystyle ∂z/∂x$$ and $$\displaystyle ∂z/∂y,$$ given $$\displaystyle x^2e^y−yze^x=0.$$. To find the equation of the tangent line, we use the point-slope form (Figure $$\PageIndex{5}$$): \[\begin{align*} y−y_0 =m(x−x_0)\\[4pt]y−1 =\dfrac{7}{4}(x−2) \\[4pt] y =\dfrac{7}{4}x−\dfrac{7}{2}+1\\[4pt] y =\dfrac{7}{4}x−\dfrac{5}{2}.\end{align*}. Viewed 24 times 1 $\begingroup$ I've been stuck on this for a couple of days. THE CHAIN RULE. Determine the number of branches that emanate from each node in the tree. {\displaystyle '=\cdot g'.} which is the same result obtained by the earlier use of implicit differentiation. The variables $$\displaystyle x$$ and $$\displaystyle y$$ that disappear in this simplification are often called intermediate variables: they are independent variables for the function $$\displaystyle f$$, but are dependent variables for the variable $$\displaystyle t$$. (You can think of this as the mountain climbing example where f(x,y) isheight of mountain at point (x,y) and the path g(t) givesyour position at time t.)Let h(t) be the composition of f with g (which would giveyour height at time t):h(t)=(f∘g)(t)=f(g(t)).Calculate the derivative h′(t)=dhdt(t)(i.e.,the change in height) via the chain rule. This branch is labeled $$\displaystyle (∂z/∂y)×(dy/dt)$$. g (t) = f (x (t), y (t)), how would I find g ″ (t) in terms of the first and second order partial derivatives of x, y, f? ∂z ∂y = … In this section, we study extensions of the chain rule and learn how to take derivatives of compositions of functions of more than one variable. $$\displaystyle z=f(x,y)=4x^2+3y^2,x=x(t)=\sin t,y=y(t)=\cos t$$, $$\displaystyle z=f(x,y)=\sqrt{x^2−y^2},x=x(t)=e^{2t},y=y(t)=e^{−t}$$, $$\displaystyle \dfrac{∂z}{∂x}=\dfrac{x}{\sqrt{x^2−y^2}}$$, $$\displaystyle \dfrac{∂z}{∂y}=\dfrac{−y}{\sqrt{x^2−y^2}}$$, $$\displaystyle \dfrac{dx}{dt}=−e^{−t}.$$. The following chain rule examples show you how to differentiate (find the derivative of) many functions that have an “inner function” and an “outer function.”For an example, take the function y = √ (x 2 – 3). This gives us Equation. and g. : Dh(a) = D(f ∘ g)(a) = Df (g(a))Dg(a). Iterated Integrals and Area; Double Integration and Volume State the chain rules for one or two independent variables. Our mission is to provide a free, world-class education to anyone, anywhere. However, it may not always be this easy to differentiate in this form. The biggest difference in the multivariable case is that the ordinary derivative has been replaced with the derivative matrix. The method involves differentiating both sides of the equation defining the function with respect to $$\displaystyle x$$, then solving for $$\displaystyle dy/dx.$$ Partial derivatives provide an alternative to this method. The notation df /dt tells you that t is the variables \end{align*} \]. Differentiating vector-valued functions (articles). Conic Sections \end{align*}\], The left-hand side of this equation is equal to $$\displaystyle dz/dt$$, which leads to, $\dfrac{dz}{dt}=f_x(x_0,y_0)\dfrac{dx}{dt}+f_y(x_0,y_0)\dfrac{dy}{dt}+\lim_{t→t_0}\dfrac{E(x(t),y(t))}{t−t_0}. The answer is yes, as the generalized chain rule states. ... [Multivariable Calculus] Taking the second derivative with the chain rule. Answer: treating everything other than t as a constant, by either the chain rule or the quotient rule you get xq(eq1)/(1 + xtq)2. To reduce it to one variable, use the fact that $$\displaystyle x(t)=\sin t$$ and $$y(t)=\cos t.$$ We obtain, \[\displaystyle \dfrac{dz}{dt}=8x\cos t−6y\sin t=8(\sin t)\cos t−6(\cos t)\sin t=2\sin t\cos t. \nonumber$. \end{align*}\]. This proves the chain rule at $$\displaystyle t=t_0$$; the rest of the theorem follows from the assumption that all functions are differentiable over their entire domains. \end{align*}\]. If z = f(x,y) = xexy, then the partial derivatives are ∂z ∂x = exy +xyexy (Note: Product rule (and chain rule in the second term) ∂z ∂y = x2exy (Note: No product rule, but we did need the chain rule) 4. If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked. We then subtract $$\displaystyle z_0=f(x_0,y_0)$$ from both sides of this equation: \begin{align*} z(t)−z(t_0) =f(x(t),y(t))−f(x(t_0),y(t_0)) \\[4pt] =f_x(x_0,y_0)(x(t)−x(t_0))+f_y(x_0,y_0)(y(t)−y(t_0))+E(x(t),y(t)). We now practice applying the Multivariable Chain Rule. These rules are also known as Partial Derivative rules. Equation \ref{implicitdiff1} can be derived in a similar fashion. \end{align*}. This multivariable calculus video explains how to evaluate partial derivatives using the chain rule and the help of a tree diagram. \begin{align*} \dfrac{∂w}{∂t} =\dfrac{∂w}{∂x}\dfrac{∂x}{∂t}+\dfrac{∂w}{∂y}\dfrac{∂y}{∂t}+\dfrac{∂w}{∂z}\dfrac{∂z}{∂t} \\[4pt] \dfrac{∂w}{∂u} =\dfrac{∂w}{∂x}\dfrac{∂x}{∂u}+\dfrac{∂w}{∂y}\dfrac{∂y}{∂u}+\dfrac{∂w}{∂z}\dfrac{∂z}{∂u} \\[4pt] \dfrac{∂w}{∂v} =\dfrac{∂w}{∂x}\dfrac{∂x}{∂v}+\dfrac{∂w}{∂y}\dfrac{∂y}{∂v}+\dfrac{∂w}{∂z}\dfrac{∂z}{∂v}. Alternatively, by letting F = f ∘ g, one can also … Free ebook http://tinyurl.com/EngMathYT Example on the chain rule for second order partial derivatives of multivariable functions. Solution A: We'll use theformula usingmatrices of partial derivatives:Dh(t)=Df(g(t))Dg(t). \end{align*}, Next, we substitute $$\displaystyle x(u,v)=3u+2v$$ and $$\displaystyle y(u,v)=4u−v:$$, \begin{align*} \dfrac{∂z}{∂u} =10x+2y \\[4pt] =10(3u+2v)+2(4u−v) \\[4pt] =38u+18v. We also acknowledge previous National Science Foundation support under grant numbers 1246120, 1525057, and 1413739. Since the first limit is equal to zero, we need only show that the second limit is finite: \[ \begin{align*} \lim_{(x,y)→(x_0,y_0)} \dfrac{\sqrt{ (x−x_0)^2+(y−y_0)^2 }} {t−t+0} =\lim_{(x,y)→(x_0,y_0)} \sqrt{ \dfrac { (x−x_0)^2+(y−y_0)^2 } {(t−t_0)^2} } \\[4pt] =\lim_{(x,y)→(x_0,y_0)}\sqrt{ \left(\dfrac{x−x_0}{t−t_0}\right)^2+\left(\dfrac{y−y_0}{t−t_0}\right)^2} \\[4pt] =\sqrt{ \left[\lim_{(x,y)→(x_0,y_0)} \left(\dfrac{x−x_0}{t−t_0}\right)\right]^2+\left[\lim_{(x,y)→(x_0,y_0)} \left(\dfrac{y−y_0}{t−t_0}\right)\right]^2}. Donate or volunteer today! The same thing is true for multivariable calculus, but this time we have to deal with more than one form of the chain rule. We want to describe behavior where a variable is dependent on two or more variables. ... Browse other questions tagged multivariable-calculus partial-differential-equations or … \end{align*}. For more information contact us at info@libretexts.org or check out our status page at https://status.libretexts.org. \nonumber\]. \end{align*}\]. Next, we calculate $$\displaystyle ∂w/∂v$$: \begin{align*} \dfrac{∂w}{∂v} =\dfrac{∂w}{∂x}⋅\dfrac{∂x}{∂v}+\dfrac{∂w}{∂y}⋅\dfrac{∂y}{∂v}+\dfrac{∂w}{∂z}⋅\dfrac{∂z}{∂v} \\[4pt] =(6x−2y)e^u\cos v−2x(−e^u\sin v)+8z(0), \end{align*}. \end{align*}\]. Then $$\displaystyle f(x,y)=x^2+3y^2+4y−4.$$ The ellipse $$\displaystyle x^2+3y^2+4y−4=0$$ can then be described by the equation $$\displaystyle f(x,y)=0$$. y ( t) y (t) y(t) y, left parenthesis, t, right parenthesis. Given the following information use the Chain Rule to determine ∂w ∂t ∂ w ∂ t and ∂w ∂s ∂ w ∂ s. w = √x2+y2 + 6z y x = sin(p), y = p +3t−4s, z = t3 s2, p = 1−2t w = x 2 + y 2 + 6 z y x = sin (p), y = p + 3 t − 4 s, z = t 3 s 2, p = 1 − 2 t Solution Assume that all the given functions have continuous second-order partial derivatives. I ended up writing, you know, maybe I wrote slightly more here, but actually the amount of calculations really was pretty much the same. Limits describe where a function is going; derivatives describe how fast the function is going.. 2.1 Instantaneous Rates of Change: The Derivative; 2.2 Interpretations of the Derivative To find $$\displaystyle ∂z/∂v,$$ we use Equation \ref{chain2b}: \begin{align*} \dfrac{∂z}{∂v} =\dfrac{∂z}{∂x}\dfrac{∂x}{∂v}+\dfrac{∂z}{∂y}\dfrac{∂y}{∂v} \\[4pt] =2(6x−2y)+(−1)(−2x+2y) \\[4pt] =14x−6y. Use tree diagrams as an aid to understanding the chain rule for several independent and intermediate variables. $$\displaystyle \dfrac{∂z}{∂u}=0,\dfrac{∂z}{∂v}=\dfrac{−21}{(3\sin 3v+\cos 3v)^2}$$. In this equation, both f(x) and g(x) are functions of one variable. The chain rule for derivatives can be extended to higher dimensions. Consider driving an off-road vehicle along a dirt road. \[ \begin{align*} z =f(x,y)=x^2−3xy+2y^2 \\[4pt] x =x(t)=3\sin2t,y=y(t)=4\cos 2t \end{align*}. Consider the ellipse defined by the equation $$\displaystyle x^2+3y^2+4y−4=0$$ as follows. Active 13 days ago. Calculate $$\displaystyle ∂z/∂u$$ and $$\displaystyle ∂z/∂v$$ given the following functions: $z=f(x,y)=\dfrac{2x−y}{x+3y},\; x(u,v)=e^{2u}\cos 3v,\; y(u,v)=e^{2u}\sin 3v. We wish to prove that $$\displaystyle z=f(x(t),y(t))$$ is differentiable at $$\displaystyle t=t_0$$ and that Equation \ref{chain1} holds at that point as well. \nonumber$. \label{chian2b}\]. hi does anyone know why the 2nd derivative chain rule is as such? If you are comfortable forming derivative matrices, multiplying matrices, and using the one-variable chain rule, then using the chain rule \eqref{general_chain_rule} doesn't require memorizing a series of formulas and determining which formula applies to a given problem. The Multivariable Chain Rule Nikhil Srivastava February 11, 2015 The chain rule is a simple consequence of the fact that di erentiation produces the linear approximation to a function at a point, and that the derivative is the coe cient appearing in this linear approximation. \dfrac { d y } { d x } = \left. Find ∂2z ∂y2. Limit Definition of the Derivative; Mean Value Theorem; Partial Fractions; Product Rule; Quotient Rule; Riemann Sums; Second Derivative; Special Trigonometric Integrals; Tangent Line Approximation; Taylor's Theorem; Trigonometric Substitution; Volume; Multivariable Calculus. i roughly know that if u = f(x,y) and x=rcos(T) , y = rsin(T) then du/dr = df/dx * dx/dr + df/dy * dy/dr but if i am going to have a second d/dr, then how does it work out? The chain rule for this case is, dz dt = ∂f ∂x dx dt + ∂f ∂y dy dt d z d t = ∂ f ∂ x d x d t + ∂ f ∂ y d y d t. So, basically what we’re doing here is differentiating f f with respect to each variable in it and then multiplying each of these by the derivative of that variable with respect to t t. \end{align*}. What factors determine how quickly your elevation rises and falls? Note: we use the regular ’d’ for the derivative. and write out the formulas for the three partial derivatives of $$\displaystyle w$$. The LibreTexts libraries are Powered by MindTouch® and are supported by the Department of Education Open Textbook Pilot Project, the UC Davis Office of the Provost, the UC Davis Library, the California State University Affordable Learning Solutions Program, and Merlot. [Multivariable Calculus] Taking the second derivative with the chain rule. Evaluating at the point (3,1,1) gives 3(e1)/16. In single-variable calculus, we found that one of the most useful differentiation rules is the chain rule, which allows us to find the derivative of the composition of two functions. If you're seeing this message, it means we're having trouble loading external resources on our website. If you are going to follow the above Second Partial Derivative chain rule then there’s no question in the books which is going to worry you. Chain Rules for One or Two Independent Variables Recall that the chain rule for the derivative of a composite of two functions can be written in the form d dx(f(g(x))) = f′ (g(x))g′ (x). Chain Rule for Second Order Partial Derivatives To ﬁnd second order partials, we can use the same techniques as ﬁrst order partials, but with more care and patience! \nonumber\], \begin{align*} \lim_{t→t_0}\dfrac{E(x(t),y(t))}{t−t_0} =\lim_{t→t_0}\dfrac{(E(x,y)}{\sqrt{(x−x_0)^2+(y−y_0)^2}}\dfrac{\sqrt{(x−x_0)^2+(y−y_0)^2}}{t−t_0}) \\[4pt] =\lim_{t→t_0}\left(\dfrac{E(x,y)}{\sqrt{(x−x_0)^2+(y−y_0)^2}}\right)\lim_{t→t_0}\left(\dfrac{\sqrt{(x−x_0)^2+(y−y_0)^2}}{t−t_0}\right). As you drive, your elevation likely changes. Starting from the left, the function $$\displaystyle f$$ has three independent variables: $$\displaystyle x,y$$, and $$\displaystyle z$$. Calculate $$\displaystyle ∂z/∂x,∂z/dy,dx/dt,$$ and $$\displaystyle dy/dt$$, then use Equation \ref{chain1}. \frac { 2 x + y + 7 } { 2 y - x + 3 } \right| _ { ( 3 , - 2 ) } = \dfrac { 2 ( 3 ) + ( - 2 ) + 7 } { 2 ( - 2 ) - ( 3 ) + 3 } = - \dfrac { 11 } { 4 } \nonumber, Equation of the tangent line: $$\displaystyle y=−\dfrac{11}{4}x+\dfrac{25}{4}$$, $$\displaystyle \dfrac{dz}{dt}=\dfrac{∂z}{∂x}⋅\dfrac{dx}{dt}+\dfrac{∂z}{∂y}⋅\dfrac{dy}{dt}$$, $$\displaystyle \dfrac{dz}{du}=\dfrac{∂z}{∂x}⋅\dfrac{∂x}{∂u}+\dfrac{∂z}{∂y}⋅\dfrac{∂y}{∂u}\dfrac{dz}{dv}=\dfrac{∂z}{∂x}⋅\dfrac{∂x}{∂v}+\dfrac{∂z}{∂y}⋅\dfrac{∂y}{∂v}$$, $$\displaystyle \dfrac{∂w}{∂t_j}=\dfrac{∂w}{∂x_1}\dfrac{∂x_1}{∂t_j}+\dfrac{∂w}{∂x_2}\dfrac{∂x_1}{∂t_j}+⋯+\dfrac{∂w}{∂x_m}\dfrac{∂x_m}{∂t_j}$$. Chapter 1 introduced the most fundamental of calculus topics: the limit. The exact same issue is true for multivariable calculus, yet this time we must deal with over 1 form of the chain rule. When you compute df /dt for f(t)=Cekt, you get Ckekt because C and k are constants. Watch the recordings here on Youtube! 10.1 Limits; 10.2 First-Order Partial Derivatives; 10.3 Second-Order Partial Derivatives; 10.4 Linearization: Tangent Planes and Differentials; 10.5 The Chain Rule; 10.6 Directional Derivatives and the Gradient; 10.7 Optimization; 10.8 Constrained Optimization: Lagrange Multipliers To derive the formula for $$\displaystyle ∂z/∂u$$, start from the left side of the diagram, then follow only the branches that end with $$\displaystyle u$$ and add the terms that appear at the end of those branches. \end{align*}\]. Suppose $$\displaystyle x=g(u,v)$$ and $$\displaystyle y=h(u,v)$$ are differentiable functions of $$\displaystyle u$$ and $$\displaystyle v$$, and $$\displaystyle z=f(x,y)$$ is a differentiable function of $$\displaystyle x$$ and $$\displaystyle y$$. Then, $$\displaystyle z=f(g(u,v),h(u,v))$$ is a differentiable function of $$\displaystyle u$$ and $$\displaystyle v$$, and, $\dfrac{∂z}{∂u}=\dfrac{∂z}{∂x}\dfrac{∂x}{∂u}+\dfrac{∂z}{∂y}\dfrac{∂y}{∂u} \label{chain2a}$, \dfrac{∂z}{∂v}=\dfrac{∂z}{∂x}\dfrac{∂x}{∂v}+\dfrac{∂z}{∂y}\dfrac{∂y}{∂v}. Active 13 days ago. The interpretation of the first derivative remains the same, but there are now two second order derivatives to consider. Solution: We will ﬁrst ﬁnd ∂2z ∂y2. To find $$\displaystyle ∂z/∂u,$$ we use Equation \ref{chain2a}: \[\begin{align*} \dfrac{∂z}{∂u} =\dfrac{∂z}{∂x}⋅\dfrac{∂x}{∂u}+\dfrac{∂z}{∂y}⋅\dfrac{∂y}{∂u} \\[4pt] =3(6x−2y)+4(−2x+2y) \\[4pt] =10x+2y. Express the final answer in terms of $$\displaystyle t$$. » Clip: Total Differentials and Chain Rule (00:21:00) From Lecture 11 of 18.02 Multivariable Calculus, Fall 2007 Flash and JavaScript are required for this feature. be defined by g(t)=(t3,t4)f(x,y)=x2y. In this diagram, the leftmost corner corresponds to $$\displaystyle z=f(x,y)$$. Further Mathematics—Pending OP Reply. Calculate $$\displaystyle ∂f/dx$$ and $$\displaystyle ∂f/dy$$, then use Equation \ref{implicitdiff1}. dt. \end{align*}, As $$\displaystyle t$$ approaches $$\displaystyle t_0, (x(t),y(t))$$ approaches $$\displaystyle (x(t_0),y(t_0)),$$ so we can rewrite the last product as, \[\displaystyle \lim_{(x,y)→(x_0,y_0)}\dfrac{(E(x,y)}{\sqrt{(x−x_0)^2+(y−y_0)^2}}\lim_{(x,y)→(x_0,y_0)}(\dfrac{\sqrt{(x−x_0)^2+(y−y_0)^2}}{t−t_0}). Find $$\displaystyle dy/dx$$ if $$\displaystyle y$$ is defined implicitly as a function of $$\displaystyle x$$ by the equation $$\displaystyle x^2+xy−y^2+7x−3y−26=0$$. This pattern works with functions of more than two variables as well, as we see later in this section. Multivariable Chain Rules allow us to differentiate $z$ with respect to any of the variables involved: Let $x=x(t)$ and $y=y(t)$ be differentiable at $t$ and suppose that $z=f(x,y)$ is differentiable at the point $(x(t),y(t))$. $$\newcommand{\id}{\mathrm{id}}$$ $$\newcommand{\Span}{\mathrm{span}}$$ $$\newcommand{\kernel}{\mathrm{null}\,}$$ $$\newcommand{\range}{\mathrm{range}\,}$$ $$\newcommand{\RealPart}{\mathrm{Re}}$$ $$\newcommand{\ImaginaryPart}{\mathrm{Im}}$$ $$\newcommand{\Argument}{\mathrm{Arg}}$$ $$\newcommand{\norm}{\| #1 \|}$$ $$\newcommand{\inner}{\langle #1, #2 \rangle}$$ $$\newcommand{\Span}{\mathrm{span}}$$, 14.5: The Chain Rule for Multivariable Functions, [ "article:topic", "generalized chain rule", "intermediate variable", "license:ccbyncsa", "showtoc:no", "authorname:openstaxstrang" ], $$\newcommand{\vecs}{\overset { \rightharpoonup} {\mathbf{#1}} }$$ $$\newcommand{\vecd}{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}}$$$$\newcommand{\id}{\mathrm{id}}$$ $$\newcommand{\Span}{\mathrm{span}}$$ $$\newcommand{\kernel}{\mathrm{null}\,}$$ $$\newcommand{\range}{\mathrm{range}\,}$$ $$\newcommand{\RealPart}{\mathrm{Re}}$$ $$\newcommand{\ImaginaryPart}{\mathrm{Im}}$$ $$\newcommand{\Argument}{\mathrm{Arg}}$$ $$\newcommand{\norm}{\| #1 \|}$$ $$\newcommand{\inner}{\langle #1, #2 \rangle}$$ $$\newcommand{\Span}{\mathrm{span}}$$ $$\newcommand{\id}{\mathrm{id}}$$ $$\newcommand{\Span}{\mathrm{span}}$$ $$\newcommand{\kernel}{\mathrm{null}\,}$$ $$\newcommand{\range}{\mathrm{range}\,}$$ $$\newcommand{\RealPart}{\mathrm{Re}}$$ $$\newcommand{\ImaginaryPart}{\mathrm{Im}}$$ $$\newcommand{\Argument}{\mathrm{Arg}}$$ $$\newcommand{\norm}{\| #1 \|}$$ $$\newcommand{\inner}{\langle #1, #2 \rangle}$$ $$\newcommand{\Span}{\mathrm{span}}$$, 14.4: Tangent Planes and Linear Approximations, 14.6: Directional Derivatives and the Gradient, Massachusetts Institute of Technology (Strang) & University of Wisconsin-Stevens Point (Herman), Chain Rules for One or Two Independent Variables. The following chain rule examples show you how to differentiate (find the derivative of) many functions that have an “inner function” and an “outer function.”For an example, take the function y = √ (x 2 – 3). In Note, $$\displaystyle z=f(x,y)$$ is a function of $$\displaystyle x$$ and $$\displaystyle y$$, and both $$\displaystyle x=g(u,v)$$ and $$\displaystyle y=h(u,v)$$ are functions of the independent variables $$\displaystyle u$$ and $$\displaystyle v$$. where the ordinary derivatives are evaluated at $$\displaystyle t$$ and the partial derivatives are evaluated at $$\displaystyle (x,y)$$. , here's what the multivariable chain rule says: d d t f ( x ( t), y ( t)) ⏟ Derivative of composition function ⁣ ⁣ ⁣ ⁣ ⁣ ⁣ = ∂ f ∂ x d x d t + ∂ f ∂ y d y d t. It is often useful to create a visual representation of Equation for the chain rule. To use the chain rule, we again need four quantities—$$\displaystyle ∂z/∂x,∂z/dy,dx/dt,$$ and $$\displaystyle dy/dt:$$. If we take the ordinary derivative, with respect to t, of a composition of a multivariable function, in this case just two variables, x of t, y of t, where we're plugging in two intermediary functions, x of t, y of t, each of which just single variable, the result is that we take the partial derivative, with respect to x, and we multiply it by the derivative of x with respect to t, and then we add to that the partial derivative with … The proof of this theorem uses the definition of differentiability of a function of two variables.