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I dont understand the example in my book,

it says; use the formula for sin(A+B) and sin(A-B) to derive the result that;

[itex] sinP + sinQ = 2sin\frac{P+Q}{2} cos\frac{P-Q}{2} [/itex]

[itex] sin(A+B) = sinAcosB + cosAcosB [/itex]

[itex] sin(A-B) = sinAcosB-cosAsinB [/itex]

Add the two intenties to get;

[itex] sin(A+B) + sin(A-B) 2sinAcosB [/itex]

let A+B = P and A-B=Q

then [itex] A = \frac{p+q}{2} [/itex] and [itex] B = \frac{P-Q}{2} [/itex]

This is the bit I dont get, How did they get this bit ^^. I understand that the LHS becomes sinP+sinQ but don't understand how they got the fraction?

[itex] sinP + sinQ = 2sin\frac{P+Q}{2} cos\frac{P-Q}{2} [/itex]

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# Trig factor formula proof help.

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