Find the area of a square with a diagonal of 8cm.

You have to use the Pythagorean theorem but there is a little twist here since a square has has equal sides. So:

x^2+x^2=8

2x^2=8

2/2x^2=8/2

x^2=4

√x^2=√4

x=2

The side of the square is 2.

So now the area of a square is:

Side*Side

2*2=4

The area of the square is 4 centimetres