Alright, I've got another question:
For the second question, in the answers they implicitly differentiate the equation wrt x and y and then the normal is the vector:
. I just wanna know why they always use -1 for the third element of this vector, and is there an alternate way of doing this question? And can we pick any number instead of -1?
EDIT: Sorry for being cold and not replying to your previous post IG, I was heading to uni when you replied, and I had work after. And then I've been busy with exams prep D: I'm still working on those q's, but I'm finishing off other subjects first