Invertible Matrix

If A is an Invertible Matrix, Show that det(AT A)>0

4 Answers

262
Aditya Bhutra ·

det(AT) = det (A) (transposing)

det(ATA) = det(AT)*det(A) = {det(A)}2 >0

since det(A)≠0 as the matrix is invertible

1
johncenaiit ·

@aditya, what if the matrix have imaginary terms?

then (det A)2 can be negative ...?

1
fahadnasir nasir ·

johncenaiit
That is the question? if the elements from complex numbers
this will not excepted.

1
johncenaiit ·

but complex number matrices are also invertible, if det≠0

so you must specify its a real matrix...

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