geometry
posted by Jen .
The diagonals of a rhombus are in 2:1. If the perimeter of the rhombus is 120cm, find the length of the diagonals.

Perimeter = 120 cm
Length of each side = 120/4 = 30
Let the diagonals be x and 2x.
Use Pythagoras theorem to calculate each side in terms of the half diagonals, x/2 and x.
30 = sqrt((x/2)²+x²)
Square both sides:
900 = (x/2)²+x²=(5/4)x²
x²=720
x=?