Question

cos^2x+6cosx+4=0

Answer 1

\(\bf cos^2(x)+6cos(x)+4=0\implies [{\color{brown}{ cos(x)}}]^2+6{\color{brown}{ cos(x)}}+4=0
\\ \quad \\
\implies a^2+6a+4\)

solve it like you'd any quadratic