A rhombus with area 840 has a diagonal of length 40. What is its side length?
Area of rhombus = d1 d2 / 2
840 = 40 d2 /2
d2 = 42 1/2 of each of the diagonals form the legs of a right triangle with the side length as the hypotenuse
20^2 + 21^2 = s^2 s = 29