SOLUTION: Which expression is equivalent to cos(1.4x) − cos(0.6x)? a. -2sin x sin(0.4x) b. 2sin x sin(0.4x) c. -2cos x cos(0.4x) d. 2cos x cos(0.4x)

Algebra ->  Finance -> SOLUTION: Which expression is equivalent to cos(1.4x) − cos(0.6x)? a. -2sin x sin(0.4x) b. 2sin x sin(0.4x) c. -2cos x cos(0.4x) d. 2cos x cos(0.4x)      Log On


   

Question 1172445: Which expression is equivalent to cos(1.4x) − cos(0.6x)?
a. -2sin x sin(0.4x)
b. 2sin x sin(0.4x)
c. -2cos x cos(0.4x)
d. 2cos x cos(0.4x)
Answer by math_tutor2020(3817) About Me  (Show Source):
You can put this solution on YOUR website!

The trig identity we can use is
cos%28A%29-cos%28B%29+=+-2%2Asin%28%28A%2BB%29%2F2%29%2Asin%28%28A-B%29%2F2%29

In this case,
A = 1.4x
B = 0.6x

cos%28A%29-cos%28B%29+=+-2%2Asin%28%28A%2BB%29%2F2%29%2Asin%28%28A-B%29%2F2%29



cos%281.4x%29-cos%280.6x%29+=+-2%2Asin%28%282x%29%2F2%29%2Asin%28%280.8x%29%2F2%29

cos%281.4x%29-cos%280.6x%29+=+-2%2Asin%28x%29%2Asin%280.4x%29

Answer: Choice A