Let A be a 3 3 matrix of non-negative real elements such that A bmatrix1\\1\\1 bmatrix=3 bmatrix1\\1\\1 bmatrix. Then the maximum value of (A) is .
Answer
27
Solution
Let rows of A be (a1, a2, a3), (b1, b2, b3), (c1, c2, c3), all elements 0
Given equation each row sum =3:
a1+a2+a3=b1+b2+b3=c1+c2+c3=3
(A)=(a1b2c3+a2b3c1+a3b1c2)
-(a3b2c1+a2b1c3+a1b3c2)
a1b2c3+a2b3c1+a3b1c2 ( the subtracted terms are 0)
(a1+a2+a3)(b1+b2+b3)(c1+c2+c3)=27
( this product contains these three terms plus other non-negative terms)
Equality for A=3I, (A)=27
Answer: 27