Question

cos2x + 2 cos x + 1 = 0
Find all solutions in the interval [0, 2π).

Answer 1

it is clear that this is the same thing as
\[(\cos(x)+1)^2=0\]?

Answer 2

making \(\cos(x)+1=0\) i.e. \(\cos(x)=-1\)

Answer 3

Consider plotting this and see x values where it = 0