For 6 points, answering 5 questions is a rip-off.
However, I shall answer 7.
haha sike get noob
The equation would just be x=8 since the x of both points is 8.
It's dependent on the context. A book may ask you to find the f'(x) of a function and you may have to use a u sub in your problem which requires you to find the dy/dx of what you substitute. So in this case both would be used.
Answer:
c.
Step-by-step explanation: