Is this B? If A is an upper triangular matrix , then [tex]A^2= .
So you need to solve , ab+ bc= 21, and . It should be easy to solve for a and c and then you have a simple linear equation to solve or b. Nothing could be simpler!

 > Matrix!! not det, or absolute value.
How do I approach this? I htought about getting rid of the 25 on the bottom right to make it a triangular matrix. Then what?[/QUOTE]