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If x2/f(4a) + y2/f(a2 - 5) = 1 represents an ellipse with major axis as y – axis and f is a decreasing function then(a) a∈(-∞, 1)(b) a∈(5,∞)(c) a∈(1,4)(d) a∈(-1, 5) |
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Answer» Correct option (d) a∈(-1, 5) Explanation: x2/f(4a) + y2/f(a2 - 5) = 1 represents an ellipse f(a2 – 5) > f(4a) ( ∴ major axis is y - axis ∴ b > a) Since f is decreasing function ∴ a2–5 < 4a (f(x1) > f (x2) then x1 < x2 for decreasing function) a2 – 4a – 5 < 0 a2 – 5a + a – 5< 0 (a – 5) (a + 1) < 0 a∈(-1, 5) |
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