5x²-10x+20=0
x²-2x+4=0
(x-2)²=0
x-2=0
x1=x2=2你确定你没看错x²-x+4 2不是4是的5x²-10x+20=0除以5得x²-2x+4=0但x²-4x+4= (x-2)²那x²-2x+4=？哦哦，我粗心了，那本题无实数解哦。因为判别式Δ=(-2)²-4*4=-12<0 无实数根如果你学习过复数（虚数）了，则可以这样5x²-10x+20=0x²-2x+4=0x²-2x+1+3=0(x-1)²-(√3i)²=0(x-1+√3i)(x-1-√3i)=0（平方差公式）x-1+√3i=0或x-1-√3i=0x1=1-√3ix2=1+√3i