One side of the triangle is 7 cm, the other is 5 cm. How many cm is the third side, if the perimeter is 18 cm

In order to find the length of the third side of the triangle, we compose and solve the equation.

The condition says that one side of the triangle is 7 cm long, and the other 5 cm.We also know the perimeter of the triangle – 18 cm.

Let’s use the variable x cm to denote the length of the third side of the triangle.

And the perimeter of a triangle can be found using the following formula:

P = a + b + c;

Substitute all the values and solve the equation:

7 + 5 + x = 18;

12 + x = 18;

x = 18 – 12;

x = 6 cm is the length of the third side of the triangle.

Answer: 6 cm.