= 3x²-1+6x-2=0

= 3x²+6x-3=0

= 3x²+3x+3x-3=0

= (3x²+3x)+(3x-3)=0

= 3x(x+1)-3(x+1)=0

= (x+1)(3x-3)=0

= x+1=0 hoặc 3x-3=0

= x=1 hoặc 3x=3

                   x=1

vậy nghiệm của pt là S={1}

1.x²+7x+10= x²+5x+2x+10=(x²+5x)+(2x+10)=x(x+5)+2(x+5)

6.x²-10x+24=x²-4x-6x+24=(x²-4x)-(6x+24)=x(x-4)+6(x-4)=(x-4)(x+6)

8.x²-10x+21=x²-3x-7x+21=(x²-3x)-(7x+21)=x(x-3)+7(x-3)=(x-3)(x+7)

12.x²-8x-20=x²-10x+2x-20=(x²-10x)+(2x-20)=x(x-10)+2(x-10)=(x-10)(x+2)

13.3x²-7x-6=3x_²-9x+2x-6=(3x²-9x)+(2x-6)=3x(x-3)+2(x-3)=(x-3)(3x+2)