The+Fundamental+Identity

In trigonometry the fundamental identity is equal to sin^2 x + cos^2 x = 1.

The fundamental identity is important because if we know the value of the sine or cosine of an angle, than the identity allows us to find the value of the angle.

Example Find cos a if sin a = 3/5 and a is in quadrant one using the fundamental identity. (3/5)^2 + cos^2 a = 1 cos^2 a = 1-(9/25) cos^2 a = 16/25 cos a = + or - sqrt(16/25) cos a = 4/5 Also, the fundamental identity can be used to form additional identities. 1-cos^2 x = sin^x 1-sin^2 x = cos^x