Which is not a method

All are methods for solving.

Hope this helps!

yes because there is exactly one y value for every x value

for function there can't be more than one value for every x value

check above link.

graphically?   well, you graph them both, the solutions is where they both intersect each other, since there are two solutions, meaning they will meet twice, or namely the linear will run into the quadratic curve twice, and where they meet, those x,y coordinates are the solutions to the system.