a)x2-5x-14=(x2-7x)+(2x-14)=x(x-7)+2(x-7)=(x-7)(x+2)
b)4x2-3x-1=(4x2-4x)+(x-1)=4x(x-1)+(x-1)=(x-1)(4x+1)
c)x2-7xy+12y2=x2-7xy+12,25y2-0,25y2=(x-3,5y)2-0,25y2=(x-3,5y-0,5y)(x-3,5y+0,5y)=(x-4y)(x-2y)
d)x3-3x+2=(x3-x)-(2x-2)=(x-1)(x2+x)-2(x-1)=(x-1)(x2+x-2)=(x-1)(x2-2x+x-2)=(x-1)(x+1)(x-2)