Review question

# Can we solve $\cos\theta - \sin (2\theta) + \cos (3\theta) - \sin (4\theta) = 0$? Add to your resource collection Remove from your resource collection Add notes to this resource View your notes for this resource

Ref: R8648

## Suggestion

Give the general solutions of the following equations

1. $2\sin 3\theta - 7 \cos 2\theta + \sin \theta + 1 = 0$,

How might we reduce the number of different multiples of $\theta$?

Can we turn the LHS into a function of $\sin \theta$ alone, or of $\cos \theta$ alone?

1. $\cos\theta - \sin 2\theta + \cos 3\theta - \sin 4\theta = 0$.

How can we simplify an expression like $\cos A + \cos B$? Are there any identities that could help us?