Is corner a of this piece of a wood square (90 degrees)? the corner piece has 13in diagonal edge and 12in vertical and a 5in

I think what they want is to use Pythagorean Theorem to determine if it's 90°.
The theorem states that, if a triangle has a right angle, the hypotenuse, called "c", relates to the other sides a and b as follows:

the diagonal of the square is the hypotenuse c, so therefore c = 13 in.
we'll make a = 5, and b = 12


So it's true! since 13 = 13, the corner is in fact a right angle!!

I’m not sure i’m sorry