Question

A triangle with sides 9, 12 and 15 is similar to a triangle whose longest side is 25. Find the perimeter of the larger triangle.​

Answer 1

P = 60

Explanation:

First, to find the scale factor, or how much bigger the other shape is, you can do so by comparing the two triangles' longest sides.

25 5

---- = ----

15 3

So the larger triangle is 5/3 times bigger.

This means that all of its other sides with also be 5/3 times bigger.

So:

9 (5/3) = 45/3 = 15

12 (5/3) = 60/3 = 20

25 + 15 + 20 = 60

So the perimeter is 60.

You could have also found the perimeter of the smaller triangle, 9 + 12 + 15 = 36, then multiplied it by the scale factor, which would be:

36 (5/3) = 180/3 = 60

You would get the same thing.