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 cos b + sin a sin b
d.
sin (a + b) = sin a cos b + cos a sin b

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

Step-by-step explanation:

Using 180 as a and q as b:

cos (180 - q)  = cos 180 cos q + sin 180 sin q

cos 180 = -1

sin 180 = 0

cos (180 - q)  = (-1) cos q +  (0) sin q

cos (180 - q)  = -cos q

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step-by-step explanation: