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
then you are linearly
obtaining a solution and you only get 2 of the solutions
(see the linear graph).
the frequency (half the period) that
has 4 times
the frequency (a quarter of the period) that
Hence there are multiple intersections between
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.