To find the measure of an unknown side of a triangle, use a^2+b^2=c^2.
(Read as "a squared plus b squared equals c squared.")
The diagonal of a triangle is c.
So filling in the formula you get:
8^2 + 15^2 = c^2
8^2 = 64
15^2 = 225
64 + 225 = 289
So that means c^2 = 289.
To find c, find the square root of 289.
√289 = 17
So c = 17, which means the measure of the unknown side is 17 m.
The filled in formula:
8^2 + 15^2 = 17^2
:)
