f(x) = f(-x)
If the point on the curve (x,y) is in the first quadrant,the opposite corner of the rectangle will be (-x,y).
So,
f(x) = 2 x y
= e^(-x^2)
f'(x) = d/d x [e^−x^2]
= e^−x^2⋅d/dx [−x^2] =(−d/d x [x^2])e^−x^2 =−2 x e^−x^2
= x (-2 e^-x)
f'(x) = 0
where x = 0
So, x = 0
we only want the positive, real root here
f(0) = e^(-0)
= 1
