If R ⊂ (0, π) denote the set of values which satisfies the equation

\(2^{1 +|cosx| + |cos^2x| + |cos^3x|+.....} = 4\), then R =

a. \(\left\{\frac{-\pi}3\right\}\)

b. \(\left\{\frac{\pi}3,\frac{2\pi}3\right\}\)

c. \(\left\{\frac{-\pi}3,\frac{2\pi}3\right\}\)

d. \(\left\{\frac{\pi}3,\frac{-2\pi}3\right\}\)