## anonymous one year ago sin(a) _______ = 1/2 [sin(a+b) + sin(a-b)] a) sin(b) b) cos(a) c) cos(b) d) sin(a)

1. anonymous

@ganeshie8 @hartnn @JackJordan

2. hartnn

can you expand sin (a+b) and sin(a-b) ? know the formulas?

3. anonymous

no..haha

4. hartnn

ok, here you go! $$\Large \sin (a+b) = \sin a \cos b +\cos a \sin b$$ $$\Large \sin (a-b) = \sin a \cos b -\cos a \sin b$$ just plug these in, on the right side.

5. hartnn

like add them and see what u get...

6. hartnn

anything getting cancelld out ?

7. anonymous

idk why but i couldn't get anything from it

8. hartnn

did you add? $$\Large \sin (a+b) + \Large \sin (a-b) \\ \Large = \sin a \cos b +\cos a \sin b+ \sin a \cos b -\cos a \sin b$$ now you see any term getting cancelled out ?

9. anonymous

So when you add them, the latter terms cancel. You will be left with two lots of sin(a)cos(b) Now dividing by two, what do we get?

10. anonymous

so is it cos (b)?

11. hartnn

jack buddy! let him/her do something :P

12. hartnn

yep, sin a cos b so yeah

13. anonymous

hrtnn why'd you give him the answer? He thought it was cos b

14. hartnn

we all know who gave out the answer, so cut it out lol