u=x ⇒ du=dx
dv=sinxdx/cos^3x ⇒ v= ∫ sinxdx/cos^3x = ∫ cos^(-3)x(-d(cosx))=
=-cos^(-2)/(-2)=1/(2*cos^2x)
= (x/(2*cos^2x))|^(π/3)_(0) - ∫ ^(π/3)_(0)dx/(2*cos^2x)=
=(π/3)/(2*(1/2)^2) - 0 - ((1/2)tgx)|^(π/3)_(0)=
= [b](2π/3)- (1/2)sqrt(3)[/b]