x=1, y=1/16
x=2,y=1/64
x=3,y=1/144
x=4,y=1/256
cos π/3 = 1/2
sin π/6 = 1/2
ctg π/4 = 1
sin π/2 = 1, тогда
1/2-1/2+5*1-5*1 = 0.