If the side length of a square is 3 and the side length increases x, the area increases y, the analytic function of Y changing with X is obtained

If the side length of a square is 3 and the side length increases x, the area increases y, the analytic function of Y changing with X is obtained

(3+x)X(3+x)=y
Simplification: y = the square of X + 6x + 9
Just hold on to the square and the area is the square of the side length