# Trigg help!

1. Nov 25, 2008

### TayTayDatDude

1. The problem statement, all variables and given/known data
Use the appropriate compound angle formula to express the following as a single trigonometric function and then determine the exact value

2. Relevant equations
(sin2pi/3)(cospi) + (cos2pi)(sinpi)
sin[(2pi/3) + pi]

3. The attempt at a solution

first answer i got -sqrt3/2

unsure if it's right

Last edited: Nov 25, 2008
2. Nov 25, 2008

### Dick

What compound angle formula are you trying to use?

3. Nov 26, 2008

### Дьявол

Can you please rewrite your original expression?

Is that (sin2п/3)(cosп) + (cos2п/3)(sinп)?

If so, as I can see you used sin(A+B) i.e sin(2п/3 + п).

This is same as sin(п - п/3 + п) or sin(-п/3 + 2п) or -sin(п/3)

If so, I guess your answer is correct.