Here to find the diagonal, you would simply split the square diagonally into 2 triangles and use the Pythagorean theorem which is used on triangles: a² + b² = c² a and b are both short sides and c is the diagonal side. So since it's a square, a and b would both be 5 and you would solce for c which is the diagonal: a² + b² = c² 5² + 5² = c² square the 5s 25 + 25 = c² add the 25s 50 = c² square root both numbers to get rid of Cs 2nd power √50 = √c² √50 = c you can reduce the square root if you want but √50 should be fine. √(25 × 2) = c √(5×5×2) 5√2 = c this is the reduced root