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Find the equation of the ellipse, whose length of the major axis is 20 and foci are `(0,+-5)`. |
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Answer» Since the foci of the ellipse lie on the y-axis, it is a vertical ellipse. Let the required equation be ` x^(2)/b^(2) + y^(2)/a^(2) = 1," where " a^(2) gt b^(2).` Let ` c^(2) = (a^(2) -b^(2)).` Its foci are `(0, pm c) ` and therefore, c = 5. Also, a = length of the semi-major axis = `(1/2 xx 20) = 10.` Now, `c^(2) = (a^(2) -b^(2)) hArr b^(2) = (a^(2)-c^(2)) = (100 - 25) = 75`. Thus, `a^(2) = (10)^(2) = 100 and b^(2) = 75.` Hence, the required equation is `x^(2)/75 + y^(2)/100 = 1.` |
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