1. 50 + 3 * ( 2x - 1 ) = 71
50 + 6x - 3 = 71
6x = 71 - 50 + 3
6x = 24
x = 4
=8(cosx-cos2x)=8(cosx-2cos^x+1)=8(3/4-2*9/16+1)=8*10/16=5