tan(x) = 1
sin(2*x) = 1
0.785398163397448
x1 = -8.639379797371932
x2 = -5.497787143782138
x3 = 3.926990816987242
x4 = -2.356194490192345
x5 = 7.068583470577035
x6 = 10.21017612416683