Sections 2.5 Multiple-Angle and Product-to-Sum Formulas
- Use double-angle formulas to rewrite trigonometric expressions.
- Use power-reducing formulas to rewrite trigonometric expressions.
- Use product-to-sum and sum-to-product formulas to rewrite trigonometric equations.
The double-angle formulas follow immediately from the sum formulas.
- Find if and is in the 4th quadrant.
- Determine a formula for .
Power-reducing and Half-angle Formulas
These formulas are easily derived from the double-angle formulas.
- Rewrite in terms of 1st powers of sines and/or cosines.
- Derive a half-angle formula for .
These formulas are easy to derive from the sum and difference formulas.
- Rewrite as a sum or difference.
- Derive a sum-to-product formula and use it to solve .