1.

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)

Answer»

Correct option  (d)  a∈(-1, 5)

Explanation:

x2/f(4a) + y2/f(a2 - 5)  = 1 represents an ellipse

f(a– 5) > f(4a) ( ∴ major axis is y - axis  b > a)

Since f is decreasing function

∴ a2–5 < 4a (f(x1) > f (x2then x1 < x2  for decreasing function)

a– 4a – 5 < 0

a– 5a + a – 5< 0

(a – 5) (a + 1) < 0

a∈(-1, 5)



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