# Precalculus : Double-Angle Identities

## Example Questions

### Example Question #1 : Double Angle Identities

Find the exact value .     Explanation:

By the double angle formula   ### Example Question #1 : Double Angle Identities

Find the exact value .     Explanation:

By the double angle formula   ### Example Question #1 : Double Angle Identities

Find the exact value .     Explanation:

By the double-angula formula for cosine For this problem  ### Example Question #1 : Double And Half Angle Identities

Find the exact value .     Explanation:

By the double-angle formula for the sine function we have thus the double angle formula becomes,  ### Example Question #3 : Double Angle Identities

If , which of the following best represents ?      Explanation:

The expression is a double angle identity that can also be rewritten as: Replace the value of theta for .

The correct answer is: ### Example Question #4 : Double Angle Identities

Which expression is equivalent to ?      Explanation:

The relevant trigonometric identity is: In this case, "u" is since .

The only one that actually follows this is ### All Precalculus Resources 