1.(x^3-3x^2)/(x^2+5x+6)÷(x^3-9x)/(x^2+2x-3)*(x+2)/(2x)
=x^2(x-3)/(x+2)(x+3) * (x+3)(x-1)/x(x+3)(x-3) * (x+2)/2x
=(x-1)/2(x+3)
(1)/(a-1)+(1)/(a+1)-(a^2+1)/(a^2-1)
=(a+1+a-1)/(a²-1)-(a²+1)/(a²-1)
=(a²+2a+1)/(a²-1)
=(a+1)²/(a-1)(a+1)
=(a+1)/(a-1)