16（x-1)`-9(x+2)`
=[4(X-1)+3(X+2)][4(x-1)-3(x+2)]
=[7x+2][x-10]
9(x)四次方-1/3x
=1/3x(27X^3-1)
=1/3x(3X-1)(9X^2+3X+1)