解方程x²+4x
x²+4x-4=0
x^2+4x-4=0 <==> (x^2+4x+4)-8=0 <==> (x+2)^2-(2根2)^2=0 <==> (x+2+2根2)(x+2-2根2)=0 <==> x=-2-2(根2),或x=-2+2(根2)。