Question 245713
The diagonal would be the hypotenuse of the right triangle formed by two sides of the square and the diagonal(a line from two corners that do not form a side).
using the formula for the hypotenuse
a^2+b^2=c^2
where a=b and c=24 sqrt2

a^2+a^2=c^2
combine 
2a^2=24^2*2
divide both sides by 2
a^2=24^2
get the square root of both sides

a=24
We are not told what units we are using inches, feet,  meters or something else.