1. Pythagorean law

If the right angles are 2 and 3 respectively, then the hypotenuse should be (2 2+3 3)1/2 = root sign 13.

That is, what is the side length of a square? The root number 13, then the square area is 13.

2. Common method

Divide the big square into four triangles and a small square.

The area of four triangles is equal to 4X 1/2X2X3= 12.

The side length of a small square is 3-2= 1,

Then the area of the small square is also 1.

So the total area is 12+ 1= 13.