geometry
posted by justine .
the bases of two triangles are the same length. The altitude of the first triangle is 5 cm and the area of the second triangle is 3 times the area of the first. what is the altitude of the second triangle?

area of first = (1/2)(b)(5) = 5b/2
area of second = (1/2)(b)(h) = bh/2
but we are told that bh/2 = 3(5b/2)
multiply both sides by 2
bh = 15b
divide both sides by b
h = 15