Найти экстремум: y=2x-1/6x^3

$y= frac{2x-1}{6x^3}$
$y=(frac{2x-1}{6x^3})= frac{2*6x^3-18x^2*(2x-1)}{36x^6} = frac{12x^3-36x^3+18x^2}{36x^6} = frac{-24x^3+18x^2}{36x^6} =$ $frac{6x^2(-4x+3)}{36x^6} = frac{-4x+3}{6x^4}$
$frac{-4x+3}{6x^4} =0$
$-4x+3=0$
$-4x=-3$
$x=0.75$
$x neq 0$
$x_{max} =0.75$