(x-1)^2-4/(x+1)^2÷x^2-9/x^2+x
=(x-1+2)(x-1-2)/(x+1)^2÷(x+3)(x-3)/x(x+1)
=(x-3)/(x+1)÷(x+3)(x-3)/x(x+1)
=x/(x+3)
2a^2-18/a(a+3)-2(a+3)÷(a-3)·a(a-3)+2(3-a）/a^2-6a+9
=2(a+3)(a-3)/(a+3)(a-2)÷a(a-3)^2-2(a-3)/(a-3)^2
=2(a-3)/(a-2)÷a(a-3)^2-2/(a-3)
=2/a(a-2)(a-3)-2/(a-3)
=[2-2a(a-2)]/a(a-2)(a-3)
=(-2a^2+4a+2)/a(a-2)(a-3)
=-2(-a^2+2a+1)/a(a-2)(a-3)
你符号的表述不是很清楚希望对你有帮助!