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Could someone help me out with this question please?

help.PNG
Original post by scientific222
Could someone help me out with this question please?

help.PNG


Have you used the identities on the LHS?
Original post by TenOfThem
Have you used the identities on the LHS?


I don't know the identities for (sin A + sin B) or (cos A + cos B) that they are telling me to use.
Original post by scientific222
I don't know the identities for (sin A + sin B) or (cos A + cos B) that they are telling me to use.


That is not what they are telling you to use
Sin(A+B) and Cos(A+B) are

They are given in the formula book if you cannot remember them
Original post by TenOfThem
That is not what they are telling you to use
Sin(A+B) and Cos(A+B) are

They are given in the formula book if you cannot remember them


They aren't telling me to use sin (A+B) which is what I originally thought, the question is saying use the identities for sin A + sin B
Original post by scientific222
They aren't telling me to use sin (A+B) which is what I originally thought, the question is saying use the identities for sin A + sin B


Wow

Major mis-read only part

Anyway, they are on the formula sheet too
Reply 6
Original post by scientific222
Could someone help me out with this question please?

help.PNG


Use that

sin(A+B)+sin(AB)=2sinAcosB\sin(A+B) +\sin(A-B)=2\cdot \sin A \cdot \cos B

and

cos(A+B)+cos(AB)=2cosAcosB\cos(A+B) +\cos(A-B)=2\cdot \cos A \cdot \cos B


At the LHS substitute A+B=2x and A-B=2y
Original post by ztibor
...


The OP should just use the formulae that are given on the formula sheet
They are the same formulae mate
Original post by TenOfThem
Wow

Major mis-read only part

Anyway, they are on the formula sheet too


Ah I didn't realise that this was sin A + sin B = 2sin( A + B / 2)cos ( A - B / 2 )
Thanks

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