f(x) = sec(θ) tan(θ)
f ' (x) = sec(θ)*tan (θ) * tan (θ) + sec(θ)sec^2(θ) = sec(θ) [ tan^2 (θ) + sec^2 (θ) ]
Note : other answers are possible
I have no clue what the answer is. I got a different answer and I put the answer you got in and it still says it's wrong. I'm assuming there must be one way they will take the answer.
Here are some other possibilities using WolframAlpha
You might try some of the other ones....!!!