Chapter 5: Problem 11
Prove that the transpose of an orthogonal matrix is an orthogonal matrix.
/*! This file is auto-generated */ .wp-block-button__link{color:#fff;background-color:#32373c;border-radius:9999px;box-shadow:none;text-decoration:none;padding:calc(.667em + 2px) calc(1.333em + 2px);font-size:1.125em}.wp-block-file__button{background:#32373c;color:#fff;text-decoration:none}
Learning Materials
Features
Discover
Chapter 5: Problem 11
Prove that the transpose of an orthogonal matrix is an orthogonal matrix.
All the tools & learning materials you need for study success - in one app.
Get started for free
A (real or complex) scalar \(u\) is said to be an \(n\) th root of unity if \(u^{n}=1\) (a) Show that if \(u\) is an \(n\) th root of unity and \(u \neq 1\) then $$1+u++u^{2}+\cdots+u^{n-1}=0$$ \\[ \left[\text {Hint}: 1-u^{n}=(1-u)\left(1+u+u^{2}+\cdots+u^{n-1}\right)\right] \\] (b) Let \(\omega_{n}=e^{\frac{2 \pi i}{n}} .\) Use Euler's formula \(\left(e^{i \theta}=\right.\) \(\cos \theta+i \sin \theta)\) to show that \(\omega_{n}\) is an \(n\) th root of unity. (c) Show that if \(j\) and \(k\) are positive integers and if \(u=\omega_{n}^{j-1}\) and \(z=\omega_{n}^{-(k-1)},\) then \(u, z,\) and \(u z\) are all \(n\) th roots of unity.
Show that if \(U\) is an \(n \times n\) orthogonal matrix, then $$\mathbf{u}_{1} \mathbf{u}_{1}^{T}+\mathbf{u}_{2} \mathbf{u}_{2}^{T}+\cdots+\mathbf{u}_{n} \mathbf{u}_{n}^{T}=I$$
The functions \(\cos x\) and \(\sin x\) form an orthonormal \(\operatorname{set} \operatorname{in} C[-\pi, \pi] .\) If \(f(x)=3 \cos x+2 \sin x\) and \(g(x)=\cos x-\sin x\) use Corollary 5.5 .3 to determine the value of $$\langle f, g\rangle=\frac{1}{\pi} \int_{-\pi}^{\pi} f(x) g(x) d x$$
Let \(\mathbf{x}=(-1,-1,1,1)^{T}\) and \(\mathbf{y}=(1,1,5,-3)^{T}\) Show that \(\mathbf{x} \perp \mathbf{y}\). Calculate \(\|\mathbf{x}\|_{2},\|\mathbf{y}\|_{2},\|\mathbf{x}+\mathbf{y}\|_{2}\) and verify that the Pythagorean law holds.
Let \(P=A\left(A^{T} A\right)^{-1} A^{T},\) where \(A\) is an \(m \times n\) matrix of rank \(n\) (a) Show that \(P^{2}=P\) (b) Prove that \(P^{k}=P\) for \(k=1,2, \ldots\) (c) Show that \(P\) is symmetric. [Hint: If \(B\) is nonsingular, then \(\left.\left(B^{-1}\right)^{T}=\left(B^{T}\right)^{-1} .\right]\)
What do you think about this solution?
We value your feedback to improve our textbook solutions.