x-tant, ∫ ln (sect)^1/3 (sect)^2dt=1/3 ∫lnsect (sect)^2dt =
1/2lnsect *(sect)^2- 1/3∫ [ (sect)^2 sect tant]╱sect dt=
1/3 lnsect*(sect)^2-1/3 ∫ (sect)^2tant dt=...∫ tant dtant=
1/3lnset*(sect)^2-1/3 *1/2 (tant)^2+c=
1/3 [ (1+x^2)] [ln √1+x^2) ]- 1/6* x^2+c.
