How do you prove that the sum of the angles of any triangle always equals 180 degrees using trigonometric functions and identities?

Answer 1

William Robinson

To prove the sum of the angles of any triangle equals 180 degrees using trigonometric functions and identities, consider a triangle with angles A, B, and C. Using the identity for the tangent of the sum of two angles, tan(A + B) = (tan A + tan B) / (1 – tan A tan B). Since tan(C) = tan(180° – (A + B)) and tan(180° – x) = -tan(x), it follows that tan(A + B) = -tan(C). This implies that A + B + C = 180°.