Given a rhombus has a side length of 15 and one diagonal has a length of 2x. Find the length of the second diagonal in terms of x. Show all work and leave your answer in radical form.
Let 2y be the length of the second diagonal. The half-diagonals and the side of the rhombus form a right triangle. The Pythagorean theorem tells us the relationship between sides and hypotenuse is ...
 x² +y² = 15²
 y² = 225 -x²
 2y = 2√(225 -x²2) . . . . the length of the second diagonal
