y=x^2+1/x,y'=2x-1/x^2
(x² + 1/x)′ = 2x - 1/x² = (2x³-1)/x²==============[(x²+1)/x]′ = (x+1/x)′ = 1 - 1/x² = (x²-1)/x² = (x+1)(x-1)/x²
