①5x^2+6xy-8y^2=(5x-4y)(x+2y)②x的n+2次-x^n-x^2+2x-1 =x^n(x²-1)-(x-1)²=(x-1)(x^n+1+x^n-x+1)③2x^3+x^2-8x-4=x²(2x+1)-4(2x+1)=(2x+1)(x²-4）=(2x+1)(x+2)(x-2)