The diagonal makes the rectangle into two RIGHT TRIANGLES....so use the Pythagorean Theorom
a^2 + b^2 = c^2
3^2 + 2^2 = c^2 (c is the diagonal in this case....the hypotenuse of the right triangle)
9 + 4 = c ^2
13 =c^2
sqrt(13) = c (the diagonal ) sqrt 13 = 3.60555
