It is in fact an

**equation**, because

__an identity holds for all angles__.

This equation is true (RHS=LHS) only for certain angles.

The functions are periodic, hence they keep intersecting "beyond" 360 degrees.

If you calculate x from

and

then you are

__linearly__ obtaining a solution and you only get 2 of the solutions

(see the linear graph).

has

**twice** the frequency (half the period) that

has.

has

**4 times** the frequency (a quarter of the period) that

has.

Hence there are multiple intersections between

and

That's what you need to bear in mind and that's what I was allowing for

when I used E and F.

However, it's far more accurate to use the identities quoted,

as you are then solving in terms of periodic functions.

If you are answering an exam question,

remember you will not typically have access to graphing software,

so it's important to understand this.