Pythagorean Theorem
posted by david .
Which is closest to the length of the diagonal of a square whose sides measure 20 cm?
a.20 cm
b.28 cm
c.40 cm
d.200 cm

Which do you think is the right answer?
20^2 + 20^2 = c^2 
The square on the hypotenuse us equal to the sum of the squares on the other two sides....
So square the sides to figure out the square on the diagonal side, then you can work out the length of that side. 
40

40 cm