Don't know the steps in finding this derivative.
But the derivative is
The answer is:
/ 3\ / 3 / 2 \\
\x / | 2 x *\7 + 7*tan (7*x)/|
(tan(7*x)) *|3*x *log(tan(7*x)) + --------------------|
\ tan(7*x) /
/ 2 2 \
/ 3\ | / / 2 \\ 2 / 2 \ / 2 \|
\x / | 3 | 7*x*\1 + tan (7*x)/| 2 / 2 \ 49*x *\1 + tan (7*x)/ 42*x*\1 + tan (7*x)/|
x*(tan(7*x)) *|6*log(tan(7*x)) + x *|3*log(tan(7*x)) + -------------------| + 98*x *\1 + tan (7*x)/ - ---------------------- + --------------------|
| \ tan(7*x) / 2 tan(7*x) |
\ tan (7*x) /
/ 3 2 2 / 2 \ 3 \
/ 3\ | / / 2 \\ 3 / 2 \ 2 / 2 \ / / 2 \\ | 2 / 2 \ / 2 \| / 2 \ 3 / 2 \ |
\x / | 6 | 7*x*\1 + tan (7*x)/| 2 / 2 \ 1372*x *\1 + tan (7*x)/ 441*x *\1 + tan (7*x)/ 3 | 7*x*\1 + tan (7*x)/| | 2 / 2 \ 49*x *\1 + tan (7*x)/ 42*x*\1 + tan (7*x)/| 126*x*\1 + tan (7*x)/ 686*x *\1 + tan (7*x)/ 3 / 2 \ |
(tan(7*x)) *|6*log(tan(7*x)) + x *|3*log(tan(7*x)) + -------------------| + 882*x *\1 + tan (7*x)/ - ------------------------ - ----------------------- + 3*x *|3*log(tan(7*x)) + -------------------|*|6*log(tan(7*x)) + 98*x *\1 + tan (7*x)/ - ---------------------- + --------------------| + --------------------- + ----------------------- + 1372*x *\1 + tan (7*x)/*tan(7*x)|
| \ tan(7*x) / tan(7*x) 2 \ tan(7*x) / | 2 tan(7*x) | tan(7*x) 3 |
\ tan (7*x) \ tan (7*x) / tan (7*x) /