For the circle

MATHEMATICS · Single correct · AP · Calculus AB · Differentiation: Composite, Implicit, and Inverse Functions · Differentiation: Composite, Implicit, and Inverse Functions

Problem

For the circle x2+y2−4x+2y=0x^{2}+y^{2}-4x+2y=0, which of the following points on the circle has a horizontal tangent? (a) (2+5, −1)(2+\sqrt{5},\,-1) (b) (0, 0)(0,\,0) (c) (2, −1+5)(2,\,-1+\sqrt{5}) (d) (2, −1)(2,\,-1)

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