2x²+4x+1=0
2x²+4x=-1
x²+2x=-1/2
x²+2x+1=-1/2+1
(x+1)²=1/2
x+1=±√(1/2)
x+1=±√2/2
x+1=√2/2或x+1=-√2/2
x=(-2+√2)/2或x=(-2-√2)/2