Description
Problem 20.1: (5.3 #8. Introduction to Linear Algebra: Strang) Suppose
⎡ ⎤ 1 1 4
A = ⎣ 1 2 2 ⎦ .
1 2 5
Find its cofactor matrix C and multiply ACT to find det(A).
⎡ ⎤
C = ⎣
6
·
−3
·
0
· ⎦ and ACT = .
· · ·
If you change a1,3 = 4 to 100, why is det(A) unchanged?
Problem 20.2: (5.3 #28.) Spherical coordinates ρ, φ, θ satisfy
x = ρ sin φ cos θ, y = ρ sin φ sin θ and z = ρ cos φ.
Find the three by three matrix of partial derivatives:
⎡ ⎤ ∂x/∂ρ ∂x/∂φ ∂x/∂θ
⎣ ∂y/∂ρ ∂y/∂φ ∂y/∂θ ⎦ .
∂z/∂ρ ∂z/∂φ ∂z/∂θ
Simplify its determinant to J = ρ2 sin φ. In spherical coordinates,
dV = ρ2 sin φ dρ dφ dθ
is the volume of an infinitesimal “coordinate box.”
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