(1) 1/(x-1)+1/(1+x)
=2x/(x^2-1)
(2) a/(a²-1)+(3a+1)/(a²-1)+(2a+3)/(1-a²)
=(a+3a+1-2a-3)/(a^2-1)
=2(a-1)/(a^2-1)
=2/(a+1)
(3) (x²-16 )/(8-2x)
=-(x+4)(x-4)/[2(x-4)]
=-(x+4)/2
=-(-2+4)/2
=-1