Answer:
58
Explanation:
We can use the Pythagorean theorem to find the area of the square for the third side.
The equation for the Pythagorean theorem is
a^2 + b^2 = c^2
where a and b are the lengths of the two legs of the triangle, and c is the length of the hypotenuse.
a^2 + b^2 = c^2
3^2+7^2=x^2
9+49=x^2
58=x^2
The area of the square for the third side of the triangle is 58 units^2 squared.