f := x -> (x+2) / (3+(x^2+1)^3); D(f); plot(f); f(0); plot(f(x), x=-5..5, y=-0.1..0.1); d := simplify(D(f)(x)); fsolve(numer(d)); s := "; D(f)(s[2]); diff(d,x); simplify("); fsolve(numer(")); plot(f(x), x=-4..0, y=-0.01..0.01);