x^3-3x^2-13x+15=x^3-3x^2+2x-15x+15
=x(x^2-3x+2)-15(x-1)
=x(x-2)(x-1)-15(x-1)
=(x-1)(x^2-2x-15)
=(x-1)(x-5)(x+3)
用因式定理分解x^3-3x^2-13x+15
x^3-3x^2-13x+15=x^3-3x^2+2x-15x+15
=x(x^2-3x+2)-15(x-1)
=x(x-2)(x-1)-15(x-1)
=(x-1)(x^2-2x-15)
=(x-1)(x-5)(x+3)