想問9.12~感謝各位高手! ^^

#12   自問自答  = ="|||
設 t = x-3 / x+1  => x = -t-3 / t-1  =>  f(t) + f( t-3 / t+1) = -t-3 / t-1
設 t = 3+x / 1-x  => x = t-3 / t+1  =>  f(-t-3 / t-1) + f(t)  = t-3 / t+1
兩式相加:  2f(x) + x = -8x / x^2 -1
f(x) = x^3+7x / 2-2x^2