- #1
Butelle
- 12
- 0
Homework Statement
Hi - i have fully worked solutions in my notes, but i do not understand this step in the proof. Proposition 3.16. Suppose that W is a subspace of a nite-dimensional inner-product
space V and let v be an alement of V . Then ||v - projW(v)|| <= ||v - w|| for all w is an element of W. Moreover, if
w element of W and ||v - projW(v)|| = ||v - w|| then projW(v) = w.
Proof. If w is an element of W then
||v - projW(v)||^2 + ||v - projW(v)||^2 + || projW(v) - w||^2 (1)
= ||v - projW(v) + projW(v) - w||^2 (by Pythagoras' Theorem) (2)
= ||v - w||^2:
note - projW(v) is the projection of v onto W
I do not really understand how (1) implies (2)? Thanks for ur help!