When we add the two equations we get:
.
Factoring gives us:
But CD + DB = BC so we have:
or
.
The area of the big square is 5*5 = 25 since each side is of length 3 + 2 = 5.
The area of each triangle is (2*3)/2 = 3.
The area of the smaller sqaure is the area of the larger sqaure minus the areas of the triangle or
25 - 4*3 = 25 -12 = 13.