Which sum or difference identity would you use to verify that cos (180° - q) = -cos q?
a. sin (a -b) = sin a cos b – cos a sin b
b. cos (a -b) = cos a cos b – sin a sin b
c. cos (a -b) = cos a cosb + sin a sin b
d. sin (a + b) = sin a cos b + cos a sin b

c. cos (a -b) = cos a cosb + sin a sin b

Step-by-step explanation:

The given identity is  

Using the formula:

We put and to get:

The correct answer is C

step-by-step explanation:

we are given

since, we have to isolate x on anyone side

so, we can move all x terms on one side

subtract both sides by 2x

add both sides by 9

divide both sides by 4

we get