# Math Help - Double Angle Identities

1. ## Double Angle Identities

Use an identity to write each expression as a trig function value or as a single number.

1-2sin^2(22 1/2 degrees)

and

1/4 - 1/2 sin^2 (47.1 degrees)

2. Hello Thatoneguy12345
Originally Posted by Thatoneguy12345
Use an identity to write each expression as a trig function value or as a single number.

1-2sin^2(22 1/2 degrees)

and

1/4 - 1/2 sin^2 (47.1 degrees)

These both use the identity $\cos2\theta =1-2\sin^2\theta$

1) $1-2\sin^222\tfrac12^o=\cos 45^o=\frac{1}{\sqrt2}$

2) $\tfrac14-\tfrac12\sin^247.1^o=\tfrac14(1-2\sin^247.1^o)=\tfrac14\cos 94.2^o$, and you can't simplify this any further.