Question

How do you find a angel when you know the sides?

Answer 1

Answer:

use The Law of Cosines first to calculate one of the angles

then use The Law of Cosines again to find another angle

and finally use angles of a triangle add to 180° to find the last angle.

cos(C) = (a2 + b2 − c2)/2ab

cos(A) = (b2 + c2 − a2)/2bc

cos(B) = (c2 + a2 − b2)/2ca

Answer 2

Answer:

Lets say its a right angle : we know that it is 90 degrees

Since  triangles are congruent to each triangle, each triangle has half as many degrees, namely 180. So this is true for any right triangle.