No, it doesn't have anything to do with a circle, it has to do with the area of a rectangle. Could please give us the entire problem. There are an infinite number of rectangles that could be positioned as you show it.
What level math are you in?
That picture wouldnt hurt.
Not a lot. First you ask for the "equasion of the shaded box". A box does not have "an equation". You might want the four inequalities that are satisfied by points in the box or you might want the area of the box. I don't know what you original problem asked for- "the equation of the shaded box" just doesn't mean anything! One problem I think you could answer is "what is the area of the largest box of this form".
What restrictions give the length of each side of the rectangle?
The base goes from -x to x, whos length is (2x). What function gives the height of the sides of the rectangle for [itex] x = x_i [/tex]
Separate names with a comma.