First of all, a bit of theory: since the area of a square is given by
[tex] A = s^2 [/tex]
where s is the length of the square. So, if we invert this function we have
[tex] s = \sqrt{A} [/tex].
Moreover, the diagonal of a square cuts the square in two isosceles right triangles, whose legs are the sides, so the diagonal is the hypothenuse and it can be found by
[tex] d = \sqrt{s^2+s^2} = \sqrt{2s^2} = s\sqrt{2} [/tex]
So, the diagonal is the side length, multiplied by the square root of 2.
With that being said, your function could be something like this:
double diagonalFromArea(double area) {
double side = Math.sqrt(area);
double diagonal = side * Math.sqrt(2);
return diagonal;
}
