Answer
$3 \sec (\dfrac{\theta}{3})+c$
Work Step by Step
Use formula $\int x^{a} dx=\dfrac{x^{a+1}}{n+1}+c$
where $c$ is a constant of proportionality.
As we know that $\int \sec x \tan x =\sec x+C$
Plug $\dfrac{\theta}{3}=a$ and $da=(\dfrac{1}{3}) d \theta$
Then, $3 \int \sec k \tan k+c=3 \sec a+c$
Hence, $3 \sec (a)=3 \sec (\dfrac{\theta}{3})+c$
