Two sides of a triangle are 8cm and 12cm long, and the altitude to the 8-cm side is 9cm. How long is the altitude to the 12-cm side?

Answer 1

We can find the area
area = (1/2)(8)(9) = 36

area using the other altitude = (1/2)(h)(12) = 6h

but the area must stay the same:
6h = 36
h = 6

Answer 2

If three sides of a triangle are 8cm,9cm and 12cm calculate the perimeter of the triangle