If the side length of a square is increased by 1cm, its area will be increased by 9cm. Find the side length of the square How to set up the equation

If the side length of a square is increased by 1cm, its area will be increased by 9cm. Find the side length of the square How to set up the equation

Let the side length be X
(x + 1) - x = 9
It's easy to get x = 4. Let's do it by ourselves