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

x is variable or an unknown value to find

example:

2x = 5 which means x = 3

we can't see all full 4 options, but if this is the full option, than the very left one is correct:

-2/5 * -3 3/4

remake the question, adding a picture of all the question, or write down the full left and right answers.