Question

How do you solve `2cos(^2)x + cosx = 0`?

Answer 1

f(x) = cos x(2cos x + 1) = 0

Solve the 2 basic trig equations: cos x = 0 and `cos x = -1/2`

Within period `(0, 2pi):`

a. cos x = 0 -> `x = pi/2 and x = (3pi)/2`

b. `cos x = -1/2 -> x = (2pi)/3 (or 120 deg) and x = (4pi)/3`(or 240 deg)