你可以返谨用因式分解悉世物法睁液x²+10x+21=0(x+3)(x+7)=0x+3=0或x+7=0x1=-3,x2=-7
x²+10x+21=0(x+3)(x+7)=0x=-3或x=-7
x^2+10x+25=4(x+5)^2=4x+5=±2x=-3或-7
(x+3)(x+7)=0x1=-3 X2=-7
