The perimeter of triangle ABC is 49 cm, side AB is 21 cm and BC is 5 cm shorter than AB Find the length AC.

1. Calculate the side of the triangle BC:

21 cm – 5 cm = 16 cm;

2. Find the side of the triangle AC:

49 cm – 21 cm – 16 cm = 28 cm – 16 cm = 12 cm.

Check (find the perimeter of the triangle using the formula):

P = a + b + c, where

P is the perimeter of the triangle,

a, b and c are its sides.

P = 21 + 16 + 12 = 37 + 12 = 49 cm.