Calculus midterm exam help. I received my grade for my calculus midterm and according to my professor I answered the two following questions incorrectly but he refuses to tell me why. If anyone could explain to me where I went wrong I would appreciate it greatly.




According to my professor, the proof used in the first question is insufficient. For the second question, he claims my answer is incorrect and should be (3cos(t), 3sin(t), t).
Thank you guys for your help!

For question 1
I imagine that your professor was expecting you to provide a cartesian equation of the plane in the form $ax + by +cz = 0$. So you should expand what you wrote with $ \vec r = x \vec i + y \vec j +z \vec k$.
For question 2
Your initial speed is incorrect and equal to $6 \vec j$.
