Question

How does this:
(x^2-2x)+(y^2+4y)=7

become this:

(x^2-2x+1) + (y^2 +4y+4)= 7+1+4?

Answer 1

complete the square for x and y

Answer 2

how does (x^2-2x+1) + (y^2 +4y+4)= 7+1+4 become (x^2-2x)+(y^2+4y)=7 ??