Sinx=t
6t²-t-1=0
D=1+24=25
t12=(1+-5)/12=1/2 -1/3
sinx=1/2
x=(-1)^n π/6+πN
sinx=-1/3
x=-(-1)^narcsin 1/3 + πN
a²b+a+ab²+b+3ab+3=a(ab+1)+b(ab+1)+3(ab+1)=(ab+1)(a+b+3)
(cos(y+x)-cos(y-x))/2=(-sinx)*siny
[{sinx <0 ; - sinx =sinx+2cosx .{sinx ≥ 0 ; sinx = sinx +cosx.
[ {sinx <0 ;tq x = -2 .{sinx ≥ 0 ; cosx = 0 .
[x = - arctq2 +2π*k ,k∈Z ; x =π/2 +2π*k ,k∈Z.