Find the length of the third side of the triangle if its perimeter is 12 cm and the lengths

Find the length of the third side of the triangle if its perimeter is 12 cm and the lengths of the other sides are 3 cm and 4 cm.

Let the length of the unknown side be x, then the following expression is valid for the perimeter of the triangle:

x + 3 + 4 = 12.

Let’s solve the resulting equation. Let’s do the calculations on the left side:

x + 7 = 12.

Move 7 to the right side of the equation with the opposite sign:

x = 12 – 7;

x = 5

Answer: The length of the third side of the triangle is 7 cm.