Let a and b be vectors in R^n. Use the definitions of projb(a) and orthb(a) to show that orthb(a) is always orthogonal to projb(a).

a) ⟨orthb(a), projb(a)⟩ = 0
b) ⟨orthb(a), projb(a)⟩ = ||a||
c) ⟨orthb(a), projb(a)⟩ = ||b||
d) ⟨orthb(a), projb(a)⟩ = ||a - projb(a)||