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# c3 help? watch

1. can anyone help with proving that:

4sin (x + 1/6pie) sin (x - 1/6pie) = 3 - 4 cos ^2 x
2. Do you know how to expand the sine brackets?
3. Look at these two equations:

What do you get when you take the second away from the first?

Think about what values of A and B will be useful.

[If you really can't work it out, use the sine angle addition formulae; but it's a really inefficient way of doing this problem!]
4. (Original post by Potassium^2)
Do you know how to expand the sine brackets?

i've got 4 sin x + 2 + sin x - 0.5

is this right? and if so wheredo i go from here??
5. do you know that Sin(A+B)=SinACosB + CosASinB, in your case A=x , B=Pi/6
6. (Original post by Potassium^2)
do you know that Sin(A+B)=SinACosB + CosASinB, in your case A=x , B=Pi/6
i dont understand how that helps me?
7. you will get 4[(sinxcospi/6 + cosxsinpi/6)(sinxcospi/6 - cosxsinpi/6)]

now you should know numerical value of sine and cosine of pi/6
What else do you notice?
8. (Original post by Potassium^2)
you will get 4[(sinxcospi/6 + cosxsinpi/6)(sinxcospi/6 - cosxsinpi/6)]

now you should know numerical value of sine and cosine of pi/6
What else do you notice?

difference of two squares? i'm sooo bad at maths btw
9. ive done it!! thankyou all so much for your help- youre great at maths!!

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Updated: September 28, 2010
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