One side of the rectangle is 15 cm, diagonal is 25 cm Find the perimeter.

One side of the rectangle is 15 centimeters long. Then let the second side be equal to X centimeters. The diagonal of this rectangle is 25 centimeters. Let’s say we have a rectangle ABCE.
Then the triangle BAE is rectangular. In it, the side BA = 15 centimeters, the leg, and the diagonal BE = 25 centimeters is the hypotenuse of this triangle, and we must find the side AE.
By the Pythagorean theorem:
BE ^ 2 = AB ^ 2 + AE ^ 2;
AE ^ 2 = BE ^ 2 – AB ^ 2;
AE ^ 2 = 25 ^ 2 – 15 ^ 2;
AE ^ 2 = 625 – 225;
AE ^ 2 = 400;
AE = 20.
The second side of the rectangle is 20 centimeters long.
By the property of a rectangle, every two of the four sides of a rectangle are equal and parallel. The perimeter of a rectangle is the sum of all its four sides (or twice the sum of its two sides):
P = 15 + 15 + 20 + 20 = 30 + 40 = 70 (centimeters).
Or:
P = 2 * (15 + 20) = 2 * 35 = 70 (centimeters).
Answer: P = 70 centimeters.