x^2-3x(x-3)-9
=x²-3x-9-9
=x²-3x-18
=(x-6)(x+3)x^2-3x(x-3)-9
=x²-3x-9-9
你这怎么算的嘞？3乘以（x-3)=3x-9额，题目是3x乘以（x-3）x²-3x(x-3)-9
=x²-3x²+9x-9
=-2x²+9x-9
=(-2x²+6x)+(3x-9)
=-2x(x-3)+3(x-3)
=(x-3)(-2x+3)
=(x-3)(3-2x)