4/(x^2-16)+2/(x+4)-2/(x-4)
=4/(x^2-16)+2(x-4)/(x^2-16)-2(x+4)/(x^2-16)
=〔4+2(x-4)-2(x+4)〕/(x^2-16)
=(4+2x-8-2x-8)/(x^2-16)
=-12/(x^2-16)