El profesor se sorprenderá mucho al ver tu solución correcta😉
cos(2*x) - 2*cos(x) - 2*sin(x) = 0
x1 = -3.92699081698724
x2 = -10.2101761241668
x3 = -7.06858347057703
x4 = 8.63937979737193
x5 = 11.7809724509617
x6 = 5.49778714378214
x7 = 2.35619449019234
x8 = -0.785398163397448
x8 = -0.785398163397448