The perimeter of the parallelogram is 20 cm, and one of the sides is 3 cm. Find the lengths of the other sides.

In order to find the three unknown sides of a parallelogram, we will compose an equation and solve it using the formula for finding the perimeter of a parallelogram.

It is known from the condition that the perimeter of the parallelogram is 20 cm. The length of one of the sides is also known – 3 cm.

In a parallelogram, opposite sides are equal.

Let’s remember the formula by which they are looking for the perimeter of a parallelogram:

P = 2 (a + b);

Let x cm be the length of the unknown side.

2 (x + 3) = 20;

x + 3 = 20: 2;

x + 3 = 10;

x = 10 – 3;

x = 7 cm.

Answer: 7 cm; 3 cm; 7 cm.