∫ tan^6xsec^4x dx= ∫ tan^6xsec^2x d(tanx)= ∫ tan^6x(1 + tan^2x) d(tanx)= ∫ (tan^6x + tan^8x) d(tanx)= (1/7)tan^7x + (1/9)tan^9x + C
