b, x2-2x-y2+1
=(x-1)2-y2
(HĐT số 2)
=(x-y-1)(x+y-1)
(HĐT số 3)
c, (x2+x)2+4(x2+x)-12
=(x2+x)2+4(x2+x)+4-16
=(x2+x+2)2-16 (HĐT số 1)
=(x2+x+2-4).(x2+x+2+4)
(HĐT số 3)
=(x2+x-2).(x2+x+6)
=(x2+2x-x-2) .(x2+x+6)
=(x+2).(x-1). (x2+x+6)
a, x3+4x2-7x-10
=x3-2x2+6x2-12x+5x-10
=x2(x-2) + 6x(x-2)+5(x-2)
=(x-2)(x2+6x+5)
=(x-2)(x2+5x+x+5)
=(x-2)(x+5)(x+1)
