解1：原式=x(x-1)/(x+1)*(x+1)/x
=x-1
解2：原式=(x+3)^2/(x+3)(x-3)*(x-3)/(x+2)
=(x+3)/(x-3)*(x-3)/(x+2)
=(x+3)/(x+2)
解3：原式=2/a*a/4
=1/2