[Dulali]

Hi,
I´m having problems with what may be a basic problem:
Question Solve 8sinxcosx=3 0 to 360
My attempt:
Using cosx=1-2sin^2 x/2 so 8sinx(1-2sin^2x/2)=3 multiplying out
8sinx-16sin^3 x/2=3 but this gets me very confused.

I´ve tried keeping things simple with:
8sinxcosx=3 to sin8x=3 then sinx=3/8 then x=sin^-1 3/8
but this gives 22?
When the solutions are: 24.3, 65.7, 204.3,245.7
Therefore, confused and demotivated with trig. Any help much appreciated.

[notnek]

So what is ?

[SecretDuck]

I'll give you a clue. It involves a double angle formula.

[aznkid66]

8sinxcosx=3 to sin8x=3

This is your error.

2*sinx*cosx=sin2x

8*sinx*cosx≠sin8x

8*sinx*cosx=4*2*sinx*cosx

[Dulali]

Thanks everyone.
Aznkid66, that final line really clarified my error. Many thanks.