x²-x-2=0 x²-8x+12=0 x²+2=3x x²+4x=21

x²-x-2=0 x²-8x+12=0 x²+2=3x x²+4x=21
x²-x-2=0 x²-8x+12=0 x²+2=3x x²+4x=21

x²-x-2=0 x²-8x+12=0 x²+2=3x x²+4x=21
x²-x-2=0
(x+1)(x-2)=0
x=2 或x= -1
x²-8x+12=0
（x-2）（x-6）=0
x=2或 x=6
x²+2=3x
x²-3x+2=0
（x-1）（x-2）=0
x=1或x=2
x²+4x=21
x²+4x-21=0
(x+7)(x-3)=0
x=3或x=-7

x²-x-2=0
(x-2)(x+1)=0
x=2,x=-1
x²-8x+12=0
(x-2)(x-6)=0
x=2,x=6
x²+2=3x
(x-1)(x-2)=0
x=1,x=2
x²+4x=21
(x-3)(x+7)=0
x=3,x=-7

4（1-x)2=9(字2是指x的平方，1-x的平方乘以4 5x2-4x-12=0(x2是4(1-x)2=9 -12x=-7 2x=-3 -4x=2 3x+6=5x+10 8-8x=9 x=7

(x-2)(x+1)=0
(x-2)(x-6)=0
(x-1)(x-2)=0
(x-3)(x+7)=0