I thought of posting my questions in already created thread with a similar topic but then I thought twice, thinking that it wouldn't be easier on the mods and it would just be invading other peoples threads.

I have many questions, many. I'm reading over the notes before starting the 40 questions that are to be done by the end of the day.

Okay so this is an example of switching the equation of a circle from standard to general.

It writes the following:

(x-root2)^2+(x-root2)^2=9

x^-root2x-root2x+2+y^2+2y+1=9

x^2-2root2x+y^2+2y+1=9

x^2-2root2x+y^2+2y-6=0 answer.

Okay, so I was trying this out if i could do it on my own and I think that they don't show all the steps like the foiling and what not, but where does the y come from?

Next question (it takes a while to get an answer so I should post more than 1 question, I feel.) Oh and by the way I'm sorry for not being able to do the root sign, the laptop does not have the #keypad so I can't use any alt key functions.

Is this a equation of a circle?

x^2+y^2-4y-4=0 yes..why?

2x^2+2y^2+4x-12y+10=0 yes, (remember to divide the equation by zero) why is a circle? How?

2x^2+y^2+7x-2y=0 no. How come?