[線代] 一個習題(Positive Semi-Definite)
A is a real matrix of full rank.
Prove I - Ainv(A'A)A' is positive semi-definite, where I is identity matrix,
A' denotes the transpose of A, and inv(A'A) is the inverse of A'A.
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這題實在是沒有招式可以用，有嘗試使用定義去做，可是卡個 inverse 在中間，變不出
花樣，有人可以幫忙或者給點提示嗎？
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