Which of the following is true about the curve x2-xy+y2=3 at the point 2,1 ? A dy/dx exists at 2,1 , but there is no tangent line at that point. B dy/dx exists at 2,1 , and the tangent line at that point is horizontal. C dy/dx exists at 2,1 , and the tangent line at that point is neither hor D dy/dx does not exists at 2,1 , and the tangent line at that point is ve E dy/dx does not exists at 2,1 , and the tangent line at that point is ho
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