∫ tan⁶xsec⁴x dx
= ∫ tan⁶xsec²x * (sec²x dx)
= ∫ tan⁶x(1 + tan²x) d(tanx)
= ∫ (tan⁶x + tan⁸x) d(tanx)
= (1/7)tan⁷x + (1/9)tan⁹x + C