drawing the diagonal will give you two right triangles. The right triangle will have two sides both equal to 10. Ti find the hypotenuse (the diagonal) use the pythagorean theorem a^2 + b^2 = c^2 where a=b=10
therefore
10^2 + 10^2 = c^2
100 + 100 = c^2
200 = c^2
take the square root of both sides to find c
square root of 200 = (square root 2)(square root 100) = c
therefore 10(square root 2) = c
or
you can use a calculator to compute square root (200)
14.142 = c
