x(x+5)=200

Question

If each side of a square is increased by 5 cm, the total area of both the new square and the original square will be 200 cm^2. Approximate to the nearest tenth of a centimeter the length of each side of the original square.

Answer 1

let x be the side length of an original square.

 

If EACH side increases by 5 units, then the new square's area is (x+5)².

 

Then you have two DIFFERENT squares, and the total area will be x² + (x+5)².

 

The expression in your title is incorrect, or inapplicable.

 

In any event (either total area that I cited or just enlarged square's area), you have a quadratic equation equal to some total area, and you should be able to solve it.