____Cosb= 1/2 [ sin(a+b) + sin (a-b)

a. sinb
b. cosa
c. cosb
d. sina

Question

____Cosb= 1/2 [ sin(a+b) + sin (a-b)

a. sinb
b. cosa
c. cosb
d. sina

hartnn · Answer

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

hartnn · Answer

add the above 2 equations.

hartnn · Answer

what u get ?

anonymous · Answer

you get... 0 = 0? 0.o   wouldn't the minus and plus signs cancil?

hartnn · Answer

how u getting 0 anywhere ?

anonymous · Answer

wait... its a +b ._.     sin(a+b) - sin(a-b) =?

hartnn · Answer

sin(a+b) = sin a cos b + cos a sin b
+ sin(a-b) = sin a cos b - cos a sin b
___________________________________________
  sin(a+b) +sin (a-b)  = 2 sin a cos b + 0

did u get this ?

nubeer · Answer

subsitute sin (a+b) with sin a cos b + cos a sin b
and sin (a-b) with sin a cos b - cos a sin b

anonymous · Answer

wait .why is there a 0 ..i get everything else in that  hartnn

hartnn · Answer

cos a sin b - cos a sin b = 0

anonymous · Answer

oooh ..ty ...now continue please?

hartnn · Answer

sin(a+b) +sin (a-b)  = 2 sin a cos b
1/2 [sin(a+b) +sin (a-b)]  =  sin a cos b
and you are done.....

anonymous · Answer

do its d sina right?

hartnn · Answer

yes.

hartnn · Answer

any more doubts ?

anonymous · Answer

NO ..and i actually understood that hartnn !! :D

hartnn · Answer

thats good :)