Let f x be a quadratic polynomial with leading coefficient 1 such that f 0 = p , p ≠ 0 , and f 1 = 1 3…

Let fx be a quadratic polynomial with leading coefficient 1 such that f0=p,p0, and f1=13. If the equations fx=0 and fofofofx=0 have a common real root, then f-3 is equal to ______.

Solution

Let fx=x-αx-β

It is given that f0=pαβ=p

and f1=13   1-α1-β=13

Now let us assume that α is the common root of fx=0 and fofofof x=0

fofofof x=0

fofofof α=0

 fofof 0=0

 fofp=0

So, fp is either α or β.

Now assuming p-αp-β=α

αβ-ααβ-β=αβ-1α-1β=1

β3=1 as 1-α1-β=13

So, β=3

Now finding α by putting the value of β in 1-α1-β=13,

1-α1-3=13

α=76

So, fx=x-76x-3

So, f-3=-3-76-3-3=25

Asked in: JEE Main 2022 (25 Jul Shift 2)

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