cos(x) = cos(radical(x))
x=±√x +2πk
t²=t+2πk
t²-t=2πk
t=(1+√(1+8πk))/2
x=(8πk+2+2√(8πk+1))/4=(4πk+1±√(8πk+1))/2 k€Z
8πk+1≥0
k≥-1/8π
-1/8πk≤k≤0
k=0
x=(4πk+1±√(8πk+1))/2=(1±1)/2
x=0;1
k>0
x=(4πk+1+√(8πk+1))/2 k€N
t²=-t+2πk
t²+t-2πk=0
t=(-1+√(8πk+1))/2
√(8πk+1)≥-1
t≥0
k≥0
k=0
x=(1-1)/2=0
x=(4πk+1-√(8πk+1))/2 k€N