The sides of the rectangle are 5 and 12 cm. Will find its diagonals.

We are given a rectangle with sides 5 cm and 12 cm. Let its length be 12 cm and width 5 cm. We need to find its diagonal. We can draw a diagonal and consider one of the resulting triangles. Since all the corners of the rectangle are straight, then the triangle will turn out to be straight. We know two of his legs, which means he can find the hypotenuse according to the rule: the square of the hypotenuse is equal to the sum of the squares of the legs.
Let’s find the sum of the squares of the legs:
5 ^ 2 + 12 ^ 2 = 25 + 144 = 169.
So our hypotenuse will be equal to the root of 169. And the root of 169 is 13.
Answer: 13 cm.