2x²-4x-5=0判别式=16+40=56x=(4±2√14)/4=1±√14/2
等式两边除2，凑个1出来则x^2-2x+1-7/2=0(x-1)^2=7/2x-1=±√7/2x==±√7/2+1根号只括了7/2哈
2x^2-4x-5=0 x^2-2x+1=3.5 (x-1)^2=3.5 x-1=±√3.5 x1=1+√3.5 x2=1-√3.5 .
x=2分支2+/-根号14
