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Part of Unit Circle

Source: 1992 National High School Mathematics League, Exam One, Problem 2

February 26, 2020

Problem Statement

The equation of unit circle in Quadrant I, III, IV ((−1,0),(1,0),(0,−1),(0,1)(-1,0),(1,0),(0,-1),(0,1) included) is (A)(x+1−y2)(y+1−x2)=0\text{(A)}(x+\sqrt{1-y^2})(y+\sqrt{1-x^2})=0 (B)(x−1−y2)(y−1−x2)=0\text{(B)}(x-\sqrt{1-y^2})(y-\sqrt{1-x^2})=0 (C)(x+1−y2)(y−1−x2)=0\text{(C)}(x+\sqrt{1-y^2})(y-\sqrt{1-x^2})=0 (D)(x−1−y2)(y+1−x2)=0\text{(D)}(x-\sqrt{1-y^2})(y+\sqrt{1-x^2})=0
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