1)x2-3x+2
=x2-x-2x+2
=x(x-1)-2(x-1)
=(x-1)(x-2)
2)2x2+5x-7
=2x2-2x+7x-7
=2x(x-1)+7(x-1)
=(x-1)(2x+7)
3)x2+7x-8
=x2-x+8x-8
=x(x-1)+8(x-1)
=(x-1)(x+8)
4)x2+8x+7
=x2+x+7x+7
=x(x+1)+7(x+1)
=(x+1)(x+7)
5)2x2-5x-7
=2x2+2x-7x-7
=2x(x+1)-7(x+1)
=(x+1)(2x-7)
xong rồi !!