Let side of square 1 is a, side of square 2 is b and square of side be c.
The area of square is square of side.
Determine the area of square 1, square 2 and square 3.
[tex]A_1=a^2[/tex][tex]A_2=b^2[/tex][tex]A_3=c^2[/tex]
Now consider the right angle triangle formed by three square.
Determine the relation between sides of square by using pythagoras theorem.
[tex]\begin{gathered} c^2=a^2+b^2 \\ A_3=A_1+A_2 \end{gathered}[/tex]
So area of square 3 is equal to sum of area of square 1 and area of square 2.
Correct option is A.