Question

Which sum or difference identity would you use to verify that cos (180° - q) = -cos q?

Answer 1

You want to use the cos difference rule:
Cos ( A - B) = CosA* CosB + SinA* SinB

Answer 2

what will (a-b) be

Answer 3

So in this case your A = 180 and B = q
So simply substitute that into the above equation i wrote for you :)
Cos ( 180 - q ) = Cos180 * Cos q + Sin180 * Sin q

[note: Cos 180 = -1 and Sin 180 = 0 ]
This would mean :
Cos ( 180 - q ) = -1* Cos q + 0
therefore Cos (180 - q) = -cos q

Answer 4

ok thank you

Answer 5

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

Answer 6

so d will be the answer

Answer 7

are you sure it's d?
(hint: look at what i used... i used cos ( a - b) = cos a cos b + sin a sin b )

Answer 8

ok i got it now thanks

Answer 9

you're welcome :)