Chapter 24: Problem 22
Determine homogeneous coordinates of the points \((3,4)\) and \((-1,7)\).
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Chapter 24: Problem 22
Determine homogeneous coordinates of the points \((3,4)\) and \((-1,7)\).
These are the key concepts you need to understand to accurately answer the question.
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Show that the exterior derivative of \(\omega=A d y d z+\) \(B d z d x+C d x d y\) is the three-form $$ \left(\frac{\partial A}{\partial x}+\frac{\partial B}{\partial y}+\frac{\partial C}{\partial z}\right) d x d y d z $$
Let \(\omega\) be the two-form in \(R^{3}-\\{0\\}\) given by $$ \omega=\frac{x d y d z+y d z d x+z d x d y}{\left(x^{2}+y^{2}+z^{2}\right)^{3 / 2}} $$ Show that \(d \omega=0\) but that there is no one-form \(\eta\) such that \(d \eta=\omega\). (Hint: If there were such a one-form, then by Stokes's theorem, with \(T\) being the unit sphere, we would have \(\int_{T} \omega=\int_{T} d \eta=\int_{S} \eta=0\), because the boundary of \(T\) is empty. Then calculate \(\int_{T} \omega\) directly.)
Show that if the point \(p^{\prime}\) lies on the polar \(\pi\) of a point \(p\) with respect to a conic \(C\), then \(\pi^{\prime}\), the polar of \(p^{\prime}\), goes through \(p\). (Hint: Assume first that \(C\) is a circle.)
Calculate \(E, F, G\) on the unit sphere parametrized by \(x=\cos u \cos v, y=\cos u \sin v, z=\sin u\), and show that \(d s^{2}=d u^{2}+\cos ^{2} u d v^{2}\)
Show that if a surface is given in the form \(z=z(x, y)\), then the measure of curvature \(k\) can be expressed as $$ k=\frac{z_{x x} z_{y y}-z_{x y}^{2}}{\left(1+z_{x}^{2}+z_{y}^{2}\right)^{2}} $$ Hint: Show first that if \(X, Y, Z\) are coordinates on the unit sphere corresponding to the point \((x, y, z(x, y))\) on the given surface, then $$ \begin{aligned} &X=\frac{-z_{x}}{\sqrt{1+z_{x}^{2}+z_{y}^{2}}}, \quad Y=\frac{-z_{y}}{\sqrt{1+z_{x}^{2}+z_{y}^{2}}} \\ &Z=\frac{1}{\sqrt{1+z_{x}^{2}+z_{y}^{2}}} \end{aligned} $$
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