the expression
as a sum or difference is
and , is simplified as
.
Explanation:
We need to rewrite the expression as a sum or difference , them simplify if possible , And the expression is :
From trigonometric identity we know that

Using the above identity we get:
⇒
⇒

⇒

⇒

⇒

Therefore , the expression
as a sum or difference is
and , is simplified as
.