## anonymous one year ago Which sum or difference identity would you use to verify that sin (90° + (theta) = cos (Theta)? a. cos (a -b) = cos a cos b + sin a sin b b. sin (a +b) = sin a cos b + cos a sin b c. sin (a -b) = sin a cos b- cos a sin b d. cos (a +b) = cos a cos b - sin a sin b

1. alekos

Well. I reckon it would have to be either b or c. What do you think?

2. anonymous

It looks to be that they are asking for the sum of identities. I think, not entirely sure, but I think... So this brings me to believe it, B.

3. anonymous

its c, i think so

4. anonymous

@Krishtika Well, looking at the equation I see this. (90° + (theta)) which makes me think a+b and, I know that it is not d.

5. zepdrix

$\Large\rm \sin(90^o+\theta)=\sin90^o \cos \theta+ \cos 90^o \sin \theta$ $\Large\rm =(1) \cos \theta+ (0) \sin \theta$ Mmm ya it looks using the sum formula gives us the correct result, ya? :)

6. anonymous

@zepdrix So, Am I correct with it being B?

7. zepdrix

yes, good job \c:/

8. anonymous

Thank you @zepdrix