# Double-Angle and Half Angle Identities - PowerPoint PPT Presentation

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Double-Angle and Half Angle Identities. Double-Angle Identity. If represents the measure of an angle, then the following identities hold for all values of . If and terminates in the first quadrant, find the exact value of each function. -1.

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Double-Angle and Half Angle Identities

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## Double-Angle and Half Angle Identities

### Double-Angle Identity

• If represents the measure of an angle, then the following identities hold for all values of .

• If and terminates in the first quadrant, find the exact value of each function.

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• If and terminates in the first quadrant, find the exact value of each function.

• we must first find the

• we must find to use the identity for .

### Half-Angle Identities

• If represents the measure of an angle, then the following identities hold for all values of .

### Use a half-angle identity to find the exact value of each function.

Since 15⁰ is a first quadrant angle and sine is positive in the first quadrant, choose the positive value.

### Use a half-angle identity to find the exact value of each function.

Since 135 is a second quadrant angle and cosine is negative in the second quadrant, choose the negative value. Thus,

### Use a half-angle identity to find the exact value of

• Complete the worksheet due Wednesday