Chapter 11: Problem 67
Define the total differential of a function of two variables.
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Chapter 11: Problem 67
Define the total differential of a function of two variables.
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Consider the function \(w=f(x, y),\) where \(x=r \cos \theta\) and \(y=r \sin \theta .\) Prove each of the following. (a) \(\frac{\partial w}{\partial x}=\frac{\partial w}{\partial r} \cos \theta-\frac{\partial w}{\partial \theta} \frac{\sin \theta}{r}\) \(\frac{\partial w}{\partial y}=\frac{\partial w}{\partial r} \sin \theta+\frac{\partial w}{\partial \theta} \frac{\cos \theta}{r}\) (b) \(\left(\frac{\partial w}{\partial x}\right)^{2}+\left(\frac{\partial w}{\partial y}\right)^{2}=\left(\frac{\partial w}{\partial r}\right)^{2}+\left(\frac{1}{r^{2}}\right)\left(\frac{\partial w}{\partial \theta}\right)^{2}\)
Describe the change in accuracy of \(d z\) as an approximation of \(\Delta z\) as \(\Delta x\) and \(\Delta y\) increase.
Describe the difference between the explicit form of a function of two variables \(x\) and \(y\) and the implicit form. Give an example of each.
Find \(\partial w / \partial r\) and \(\partial w / \partial \theta\) (a) using the appropriate Chain Rule and (b) by converting \(w\) to a function of \(r\) and \(\boldsymbol{\theta}\) before differentiating. \(w=\arctan \frac{y}{x}, \quad x=r \cos \theta, \quad y=r \sin \theta\)
In Exercises 33 and \(34,\) find \(d^{2} w / d t^{2}\) using the appropriate Chain Rule. Evaluate \(d^{2} w / d t^{2}\) at the given value of \(t\) \(w=\arctan (2 x y), \quad x=\cos t, \quad y=\sin t, \quad t=0\)
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