If $X^TX=X$, show that $X=X^T=X^2$.
Can someone help me with this? I'm having trouble proving this question. Thank you.
2026-04-24 16:08:38.1777046918
Prove that if $X^TX=X$, then $X=X^T=X^2$
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From $X=X^TX$ it follows that $X^T=(X^TX)^T=X^T X^{TT}=X^TX.$