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The center of the ellipse is at (h,k). The width of the blue box is determined by a and the height is determined by b. The edges of the blue box, which is what constrains the ellipse, are at (h ± a, k ± b). Try different values of h, k, a and b to see their effect. When a = b, you have a circle. The General Form was derived by multiplying the Standard Form by a²b². It may not be fully reduced.