x的三次方加2x 再加3=（x^3+1）+（2x+2）=(x+1)(x^2-x+1)+2(x+1)=(x+1)(x^2-x+1+2)=(x+1)(x^2-x+3)
X3+2x+3= X3+1+2x+2=(x+1)( X2-x+1)+2(x+1)= (x+1)( X2-x+3)
