The sum of the roots of the equation  4cos3x−4cos2x−cosπ+x−1=0 in the interval 0,315 is pπ , where p is equal to

We have 4cos3x−4cos2x−cosπ+x−1=0            ⇒       4cos3x−4cos2x+cosx−1=0            ⇒4cos2x+1cosx−1=0             ⇒cosx=1⇒x=2nπ              We  have    100π<315<101π∴Required sum = 2π+4π+......100π                                   =21+2+....50π                                    =2×50×512π=2550π