=(1/x) +(3x^2*cosx+x^3*sinx)/cos^2x;
y``=(1/x)` +((3x^2*cosx+x^3*sinx)/cos^2x)`=
=(-1/x^2)+((3x^2*cosx+x^3*sinx)*cos^2x-(cos^2x)`*(3x^2*cosx+x^3*sinx))/(cos^4x)
y`=(-1/x^2)+ [b]([/b](6x*cosx-3x^2sinx+3x^2*sinx+x^3*cosx)*cos^2x-2cosx*(-sinx)*(3x^2*cosx+x^3*sinx)[b])[/b]/(cos^4x)
y`=(-1/x^2)+[b]([/b](6x*cosx+x^3*cosx)*cosx+2sinx*(3x^2*cosx+x^3*sinx)[b])[/b]/(cos^3x)
(-1/x^2)+[b]([/b](6x*cos^2x+x^3*cos^2x+3x^2*sin2x+2x^3*sin^2x)[b])[/b]/(cos^3x)