Let S be the set of all non - zero real numbers α such that the quadratic equation α x 2 - x +…

Let S be the set of all non - zero real numbers α such that the quadratic equation αx2-x+α=0 has two distinct real roots x1 and x2 satisfying the inequality x1-x2<1. Which of the following intervals is(are) a subset(s) of S?
  1. -12, - 15
  2. - 15, 0
  3. 0, 15
  4. 15,12

Solution

αx2-x+α=0
x1-x2<0
1-4α2α<1
1-4α2<|α|
1-4α2<α2
α2-15>0
α -, -15 15, 
Also, 1-4α2>0
α2-14<0
α-12  α+12<0
α -12,12
Taking intersection
α  -12, -15  15,12

Asked in: JEE Advanced 2015 (Paper 2)

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