ELLIPSE 1. STANDARD EQUATION & DEFINITION : Standard equation of an ellipse referred to its principal axis along the co-ordinate axis is \(\dfrac{\mathbf{x}^{2}}{\mathbf{a}^{2}}+\dfrac{\mathbf{y}^{2}}{\mathbf{b}^{2}}=\mathbf{1}\) . where \(a>b \) & \( b^{2}=a^{2}\left(1-e^{2}\right)\) \(\Rightarrow a^{2}-b^{2}=a^{2} e^{2} .\) where \(e=\) eccentricity \((0<e<1)\) . \(\mathrm{FOCI}: \mathrm{S} \equiv(\mathrm{ae}, 0) \) & \( \mathrm{~S}^{\prime} \equiv(-\mathrm{ae}, 0) .\) (a) Equation of directrices : \(\mathrm{x}=\dfrac{\mathrm{a}}{\mathrm{e}} \) & \( \mathrm{x}=-\dfrac{\mathrm{a}}{\mathrm{e}} \text { . }\) (b) Vertices: \(\mathrm{A}^{\prime} \equiv(-\mathrm{a}, 0) \quad \) & \( \mathrm{~A} \equiv(\mathrm{a}, 0)\) (c) Major axis : The line segment \(A^{\prime} A\) in which the foci \(S^{\prime}\) & S lie is of length \(2 \mathrm{a} \) & \(\) is called the major axis \((a>b)\) of the ellipse. Point of intersection of major axis with dir...
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