原式=[x/(x-3)]-[5x/(x²-x-6)] =[x/(x-3)]-(5x)/[(x-3)(x+2)]=[x(x+2)]/[(x-3)(x+2)]-(5x)/[(x-3)(x+2)]=(x²+2x-5x)/[(x-3)(x+2)]=(x²-3x)/[(x-3)(x+2)]=[x(x-3)]/[(x-3)(x+2)]=x/(x+2)