- We need to evaluate
intsin(x−α)sinxdx
and compare it with
Ax+Blogsin(x−α)+C.
- Express sinx in terms of (x−α):
sinx=sin((x−α)+α).
Using the identity
sin(u+v)=sinucosv+cosusinv,
we get
sinx=sin(x−α)cosα+cos(x−α)sinα.
- Divide by sin(x−α):
sin(x−α)sinx=cosα+sinαsin(x−α)cos(x−α).
So,
sin(x−α)sinx=cosα+sinαcot(x−α).
- Integrate term by term:
∫sin(x−α)sinxdx=∫cosαdx+sinα∫cot(x−α)dx.
Since cosα and sinα are constants,
=xcosα+sinα∫cot(x−α)dx.
Now,
∫cot(x−α)dx=log∣sin(x−α)∣.
Hence,
∫sin(x−α)sinxdx=xcosα+sinαlog∣sin(x−α)∣+C.
- Comparing with
Ax+Blogsin(x−α)+C,
we obtain
A=cosα,B=sinα.
- Therefore,
(A,B)=(cosα,sinα).
This matches option B.