Write "?" in terms of [math]\theta[/math]. What do you get?
In terms of the symbols "%", "$", and/or "!", what is [math]sin\left(\theta\right)[/math]?
In terms of the symbols "%", "$", and/or "!", what is [math]cos\left(?\right)[/math]
Take your results from (1) and (3) to write a new trigonometric identity. What do you get?
In terms of the symbols "%", "$", and/or "!", what is [math]cos\left(\theta\right)[/math]?
In terms of the symbols "%", "$", and/or "!", what is [math]sin\left(?\right)[/math]
Take your results from (1) and (6) to write a new trigonometric identity. What do you get?