Simplify the expression by using a sum or difference identity.cos(12k) cos (9k) - sin(12k) sin (9k)
A. sin(21k)
B. cos(3k)
C. sin(3k)
D. cos(21k)
Answer: D
Mathematics
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Factor out the greatest common factor.5x2 + 45x
A. 5x2(x + 9) B. 5x(x + 45) C. 5x(x + 9) D. x(5x + 45)
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Graph the function.y = 2x2 - 2x - 1
A. 
B. 
C. 
D. 
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Solve.
= -13
A. 25
B. -5, 5
C. 
D. No solution
Mathematics
Solve the problem.A propeller on a wind generator rotates 1.24 rad in 1.5 s. How many degrees does the propeller rotate in 
A. 35.5° B. 0.022° C. 71.0° D. 142°
Mathematics