Chapter 13: Problem 7
What three conditions must be met for a function \(f\) to be continuous at the point \((a, b) ?\)
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Chapter 13: Problem 7
What three conditions must be met for a function \(f\) to be continuous at the point \((a, b) ?\)
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The flow of heat along a thin conducting bar is governed by the one- dimensional heat equation (with analogs for thin plates in two dimensions and for solids in three dimensions) $$\frac{\partial u}{\partial t}=k \frac{\partial^{2} u}{\partial x^{2}},$$ where \(u\) is a measure of the temperature at a location \(x\) on the bar at time t and the positive constant \(k\) is related to the conductivity of the material. Show that the following functions satisfy the heat equation with \(k=1.\) \(u(x, t)=A e^{-a^{2} t} \cos a x,\) for any real numbers \(a\) and \(A\)
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Maximizing a sum Geometric and arithmetic means Prove that the geometric mean of a set of positive numbers \(\left(x_{1} x_{2} \cdots x_{n}\right)^{1 / n}\) is no greater than the arithmetic mean \(\left(x_{1}+\cdots+x_{n}\right) / n\) in the following cases. a. Find the maximum value of \(x y z,\) subject to \(x+y+z=k\) where \(k\) is a real number and \(x>0, y>0,\) and \(z>0 .\) Use the result to prove that $$(x y z)^{1 / 3} \leq \frac{x+y+z}{3}$$ b. Generalize part (a) and show that $$\left(x_{1} x_{2} \cdots x_{n}\right)^{1 / n} \leq \frac{x_{1}+\cdots+x_{n}}{n}$$
Use the method of your choice to ate the following limits. $$\lim _{(x, y) \rightarrow(1,0)} \frac{y \ln y}{x}$$
Consider the following equations of quadric surfaces. a. Find the intercepts with the three coordinate axes, when they exist. b. Find the equations of the \(x y-, x z^{-}\), and \(y z\) -traces, when they exist. c. Sketch a graph of the surface. $$-x^{2}+\frac{y^{2}}{4}-\frac{z^{2}}{9}=1$$
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