# Going backwards?!

Q:  Express sin9x – sin7x as a product containing only sines and/or cosines:

A. 2sinx cos8x
B. -2sinx cos8x
C. 2sin8x cos x
D. -2sin8x cosx

# More Trig Identities!

Q:  Factor the expression and use the fundamental trigonometric identities to simplify:

cos²x sec²x -cos ²x =

A. cos²x cot²x
B. cos²x
C. 1
D. sin²x

# Exact Values using identities

Q: Find the exact values:

(a)  sin(5π/12)

(b)  cos(5π/12)

(c)  tan(5π/12)

# Product-to-sum Identity Example 2

Q : Which is 2*sin(4x)*cos(2x) written as a sum containing only sines?

A. sin 6x – sin 2x

B. sin 5x – sin3x

C. sin 5x + sin 3x

D. sin 6x + sin 2x

# Product-to-Sum Identity

Q: Which of the following expresses 2cos(5x)* cos(2x) as a sum containing only sines or cosines?

A. cos(7x)-cos(3x)

B. cos(6x)+cos(4x)

C. cos(7x)+cos(3x)

D. cos(6x)-cos(4x)

# Identities to Memorize

Q:  Which expression completes the fundamental trigonometric identity ? sec(-x)

A. -sec x
B. sec x
C. cos x
D. -cos x

# Double Angle Identity

Q:  Find the exact value of sin(2a) and cos(2a) using the double angle formulas, given sin(a) = 5/9 , π/2 < a < π

# Trig Identities

Q : Which expression completes the fundamental trigonometric identity sin(π/2-u) =

A. -sec u

B. csc u

C . cos u

D. -sin u