For the curve defined by

MATHEMATICS · Single correct · A Level · Mathematics · Differentiation · Differentiation

Problem

For the curve defined by x2+xy+y2=7x^{2}+xy+y^{2}=7, determine the xx–coordinate(s) of all points where the tangent line is horizontal. (a) x=±2213x=\pm\dfrac{2\sqrt{21}}{3} (b) x=±3x=\pm 3 (c) x=±73x=\pm\sqrt{\dfrac{7}{3}} (d) x=±72x=\pm\sqrt{\dfrac{7}{2}}

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