Question

How do you use the double angle or half angle formulas to rewrite the expression sin2x + cosx as one involving only sinx and cosx?

Answer 1

Refer to explanation

Explanation:

Well we have that

`sin(x+y)=sinx*cosy+cosx*siny` hence for x=y we get

`sin2x=2sinxcosx`

Hence the quantity `sin2x+cosx` can be written as

`sin2x+cosx=2sinx*cosx+cosx=cosx*(1+2sinx)`