已知函数 f(x)=cos2x+cos3x,x∈(0,π)f\left( x\right) = \cos {2x} + \cos {3x},x \in \left( {0,\pi }\right)f(x)=cos2x+cos3x,x∈(0,π) ,若 f(x)f\left( x\right)f(x) 有两个零点 x1,x2(x1<x2){x}_{1},{x}_{2}\left( {{x}_{1} < {x}_{2}}\right)x1,x2(x1<x2) ,则( )A. 2π5∈{x1,x2}\frac{2\pi }{5} \in \left\{ {{x}_{1},{x}_{2}}\right\}52π∈{x1,x2}B. x2=2x1{x}_{2} = 2{x}_{1}x2=2x1C. cosx1+cosx2=12\cos {x}_{1} + \cos {x}_{2} = \frac{1}{2}cosx1+cosx2=21D. cosx1cosx2=32\cos {x}_{1}\cos {x}_{2} = \frac{\sqrt{3}}{2}cosx1cosx2=23