Trước tiên là bạn phải nhớ Ct: 1+tan2x=1cos2x⇒tan2x=1cos2x−1
∫tan8xdx=∫tan6x.tan2xdx=∫tan6x.(1cos2x−1)dx=∫(tan6x.1cos2x)dx−∫tan6xdx
=∫(tan6x1cos2x)dx−∫tan4x.(1cos2x−1)dx
=..................−∫tan4x1cos2xdx−∫tan4xdx
=........................................−∫tan2x(1cos2x−1)dx
=........................................−∫tan2x1cos2xdx−∫tan2xdx
.............................
như thế bạn làm tiếp được rồồi.