Explanation: 1- getting the third side: We are given that: perimeter of the triangle is 180 cm Two of its sides are 80 cm and 18 cm This means that: 180 = 80 + 18 + third side third side = 180 - (80+18) third side = 82 cm
2- deducing the shortest side that we will use to get the altitude: We have the three sides of the triangle 80 cm, 18 cm and 82 cm It is obvious that the shortest side is 18 cm We will use this side to calculate the altitude since we are given that the altitude corresponds to the shortest side.
3- getting the altitude: area of triangle = 0.5 * base * altitude We have: area of triangle = 720 cm² base = 18 cm Substitute to get the altitude as follows: 720 = 0.5 * 18 * altitude 720 = 9*altitude altitude = 80 cm
