解一元二次方程,谢

题目

解一元二次方程,谢
x2+12x=0,4x2-1=0,x2=7x,x2-4x-21=0,（x-1）（x+3）=12,3x2+2x-1=0

答案

x2+12x=0,x(x+12)=0x=0, -12 4x2-1=0,(2x+1)(2x-1)=0x=-1/2, 1/2 x2=7x,x(x-7)=0x=0, 7 x2-4x-21=0,(x-7)(x+3)=0x=7, -3 （x-1）（x+3）=12,x^2+2x-3=12x^2+2x-15=0(x+5)(x-3)=0x=-5, 3 3x2+2x-1=0(3x-1)(x+1)=0x=1/...