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Question: Answered & Verified by Expert
Let a be an integer such that all the real roots of the polynomial 2x5+5x4+10x3+10x2+10x+10 lie in the interval a,a+1. Then, |a| is equal to ______.
MathematicsApplication of DerivativesJEE MainJEE Main 2021 (26 Feb Shift 2)
Solution:
1065 Upvotes Verified Answer
The correct answer is: 2

Let 2x5+5x4+10x3+10x2+10x+10=fx

Now f-2=-34 and f-1=3

Hence fx has a root in -2,-1

Further f'x=10x4+20x3+30x2+20x+10

=10x2x2+2x+3+2x+1x2

=10x2x2+1x2+2x+1x+3

=10x2x+1x2-2+2x+1x+3

=10x2x+1x+12>0  for all x belongs to R.

fx is strictly increasing function. Since it is an odd degree polynomial it will have exactly one real root.

Hence, fx has only one real root, so a=2.

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