Question

For the rhombus ABCD, diagonal BD = 18 and diagonal AC = 24. What is the side length of the rhombus? A) 15 2 B) 21 2 C) 15 D) 21

Answer 1

The diagonals are perpendicular to each other.
The right triangle has half of each diagonal as sides, so the hypotenuse or side length is Sqrt(9^2 + 12^2) = 15.
Hint: a 3,4,5 sided triangle is the smallest integer right triangle.  Doubling or tripling, etc. is still a right triangle.  So when I saw the 9,12, I knew that 15 was the hypotenuse.