17(1)原式=(a+1)²/(a+1)(a-1)-a(a+1)/(a+1)(a-1)=(a+1)(a+1-a)/(a+1)(a-1)=1/(a-1)(2)原式=(x-2)(x-3)/(x+4)(x-4)·(-(x-4))/(x-3)·(x+1)(x+4)/(2+x)(2-x)=-(x-2)/(x+4)·(x+1)(x+4)/(2+x)(2-x)=(x+1)/(x+2)