# Thread: Find x and y so A^2 = A

1. ## Find x and y so A^2 = A

If A = x 4
.........y 7

(^^^^ that is a 2x2 matrix)

determine the values of x and y for which A^2=A.

No idea how to start this one.

i didnt think it was possible because

A^2 = x^2 16
..........y^2 49

A = x 4
......y 7

so how can A^2 ever equal A because no matter what the x and y values are, 4 and 7 will never equal 16 and 49?

Help please

Thank you

2. Originally Posted by mybrohshi5
If A = x 4
.........y 7

(^^^^ that is a 2x2 matrix)

determine the values of x and y for which A^2=A.

No idea how to start this one.

i didnt think it was possible because

A^2 = x^2 16
..........y^2 49

A = x 4
......y 7

so how can A^2 ever equal A because no matter what the x and y values are, 4 and 7 will never equal 16 and 49?

Help please

Thank you
The first thing you should do is review how to multiply matrices. Because A^2 is NOT equal to what you got. Note: $A^2 = A \times A$.

3. Duh haha thank you. its getting late here and i shouldnt be doing math when im tired. i always forget little things like that.

thank you again.