For $0\;<\;x\;<\;\pi$, the values of x which satisfies $1+|cos\;x|+|cos\;x|^2+|cos\;x|^3+$....$\infty$ = $2^4$ are
$(a)\;\frac{\pi}{3}\;,\frac{3\pi}{4}\qquad(b)\;\frac{\pi}{3}\;,\frac{2\pi}{3}\qquad(c)\;\frac{\pi}{4}\;,\frac{3\pi}{4}\qquad(d)\;None\;of\;the\;above$