The perimeter of parallelogram ABCD is 60cm, side AB is 20cm. Find the sides of the parallelogram.

In order to find the sides of a rectangle, we will recall the properties of the sides of a rectangle and the formula for finding the perimeter of a rectangle.

So, from the condition it is known that one of the sides of the rectangle is 20 cm, and its perimeter is 60 cm.

The opposite sides of the rectangle are equal to each other. That is, we know the length of one pair of sides to be 20 cm.

Let’s denote by x cm the length of the second side.

P = 2 (a + b);

2 (20 + x) = 60;

20 + x = 60: 2;

20 + x = 30;

x = 30 – 20;

x = 10 cm is the length of the second pair of sides of the rectangle.