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# C3 Trig Proof Question watch

1. Use the formula for sin(A+B) and sin(A-B) to derive the result that...

sinP + sinQ = 2sin ()cos()

It's example 20 from the C3 edexcel textbook.

I get the part up to Let A + B = P, A - B = Q

But not this next step:

then A = and B =

Surely A is P - B? I can't see why they divided by 2...thanks!
2. (a + B = P) + (a - B = Q)

A + B + A - B = P + Q

2a = P + Q

A = (p + Q)/2
3. (Original post by gottastudy)
Use the formula for sin(A+B) and sin(A-B) to derive the result that...

sinP + sinQ = 2sin ()cos()

It's example 20 from the C3 edexcel textbook.

I get the part up to Let A + B = P, A - B = Q

But not this next step:

then A = and B =

Surely A is P - B? I can't see why they divided by 2...thanks!
If P= A+B and Q=A-B

Make A the subject in P so A= P-B
Then sub it into Q so now:
Q= (P-B)-B
now make B the subject so -B = therefore B=

And do the same for P
4. I understand now! Thanks for your help!!
5. (Original post by gottastudy)
I understand now! Thanks for your help!!
You could always leave rep...
6. (Original post by JTeighty)
You could always leave rep...
I've already used mine today. You'll get it soon
7. (Original post by gottastudy)
I've already used mine today. You'll get it soon
Thanks but don't worry about it.

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