Chapter 3: Problem 3
Find a point that lies on the plane \(x+3 y+5 z=9\) and a normal vector to the plane.
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Chapter 3: Problem 3
Find a point that lies on the plane \(x+3 y+5 z=9\) and a normal vector to the plane.
These are the key concepts you need to understand to accurately answer the question.
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Let \(U\) be an open set in \(\mathbb{R}^{n}\), and let \(f: U \rightarrow \mathbb{R}\) be a function that is continuous at a point a of \(U\) (a) If \(f(\mathbf{a})>0\), show that there exists an open ball \(B=B(\mathbf{a}, r)\) centered at a such that \(f(\mathbf{x})>\frac{f(\mathbf{a})}{2}\) for all \(\mathbf{x}\) in \(B .\left(\right.\) Hint : Let \(\left.\epsilon=\frac{f(\mathbf{a})}{2} .\right)\) (b) Similarly, if \(f(\mathbf{a})<0\), show that there exists an open ball \(B=B(\mathbf{a}, r)\) such that \(f(\mathbf{x})<\frac{f(\mathbf{a})}{2}\) for all \(\mathbf{x}\) in \(B\). In particular, if \(f(\mathbf{a}) \neq 0\), there is an open ball \(B\) centered at a throughout which \(f(\mathbf{x})\) has the same sign as \(f(\mathbf{a})\).
The graph of the function \(f(x, y)=x^{3}-3 x y^{2}\) is called a monkey saddle. You will need to bring one along whenever you invite a monkey to go riding with you. The level sets of \(f\) are not easy to sketch directly, but it is still possible to get a reasonable idea of what the graph looks like. (a) Sketch the level set corresponding to \(c=0 .\) (Hint: \(\left.x^{3}-3 x y^{2}=x(x+\sqrt{3} y)(x-\sqrt{3} y) .\right)\) (b) Draw the region of the \(x y\) -plane in which \(f(x, y)>0\) and the region in which \(f(x, y)<0\). (Hint: Part (a) might help.) (c) Use the information from parts (a) and (b) to make a rough sketch of the monkey saddle.
Let \(\mathbf{v}\) and \(\mathbf{w}\) be vectors in \(\mathbb{R}^{n}\). (a) Show that \(\|\mathbf{v}\|-\|\mathbf{w}\| \leq\|\mathbf{v}-\mathbf{w}\| .(\) Hint: \(\mathbf{v}=(\mathbf{v}-\mathbf{w})+\mathbf{w} .)\) (b) Show that \(|\|\mathbf{v}\|-\|\mathbf{w}\|| \leq\|\mathbf{v}-\mathbf{w}\|\).
Sketch the surface in \(\mathbb{R}^{3}\) described by the given equation. $$ x^{2}+z^{2}=4 $$
Let \(U\) be the set of points \((x, y)\) in \(\mathbb{R}^{2}\) that satisfy the
given conditions. Sketch \(U,\) and determine whether it is an open set. Your
arguments should be at a level of rigor comparable to those given in the text.
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