### Home > PC3 > Chapter 8 > Lesson 8.3.5 > Problem8-151

8-151.
1. These expressions look complicated, but they are not if you know your trigonometric identities. Review the addition/subtraction formulas, double-angle formulas, and half-angle formulas. Then simplify each of the expressions below. Homework Help ✎

1. sin(50º) cos(20º) + cos(50º) sin(20º)

2. 2 sincos

3. cos2 – sin2

4. cos(110º) cos(50º) – sin(110º)sin(50º)

Use the angle sum formula for sine.

Use the Double-Angle formula for the cosine.

Use the Half-Angle formula for cosine.

Use the Double-Angle formula for the sine.

$\text{sin}\left( 2\left( \frac{2\pi}{5} \right) \right)$

Use the angle sum formula for the cosine.

Use the Half-Angle formula for sine.