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FIND THE COORDINATES OF THE FOCI AND THE LENGTH OF LATUS RECTUM OF(a) the hyperbola 9x2 - 16y2 =144 (b) the ellipse 3x2 + 2y2 = 18 |
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Answer» (a) Given hyperbola is 9x2 - 16y2 - 144 ⇒ \(\frac{x^2}{16}-\frac{y^2}9=1\) By comparing with \(\frac{x^2}{a^2}+\frac{y^2}{b^2}=1\) We get a2 = 16, b2 = 9 ⇒ a = 4, b = 3 \(\therefore\) e = \(\sqrt{1+\frac{b^2}{a^2}}\) = \(\sqrt{1+\frac{3^2}{4^2}}\) \(=\frac{4^2+3^2}{4^2}\) = \(\frac{5^2}{4^2}=\frac54\) \(\therefore\) coordinates of fozi are (+ae, 0) = (\(\pm\)4 x 5/4,0) = (\(\pm5,0\)) Hence, (-5, 0) and (5, 0) are coordinates of foci or given hyperbola. And latus rectum of hyperbola = \(\frac{2b^2}a=\frac{2\times9}4=\frac92\) unit (b) Given ellipse is 3x2 + 2y2 = 18 ⇒ \(\frac{x^2}6+\frac{y^2}9=1\) \(\therefore\) a2 = 6 and b2 = 9 ⇒ a = √6 and b = 3 \(\because\) b > a \(\therefore\) Focus of ellipse lies on y-axis. Now, e = \(\sqrt{1-\frac{q^2}{b^2}}=\sqrt{1-\frac69}\) = \(\sqrt{\frac{9-6}9}\) = \(\frac{\sqrt3}3\) = \(\frac1{\sqrt3}\) \(\therefore\) Co-ordinates of foci are (0, \(\pm\)be) = (0, \(\pm\)9 x \(\frac1{\sqrt3}\)) = (0, \(\pm\)\(\frac{3}{\sqrt3}\)) (0, \(\pm\sqrt3\)) Hence, (0, \(\sqrt3\)) and (0, \(-\sqrt3\)) are co-ordinates of foci or given ellipse. And latus rectum of ellipse = \(\frac{2b^2}a=\frac{2\times3}{\sqrt6}\) = \(\frac{6}{\sqrt6}\) = \(\sqrt6\) unit |
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