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Question

Question: Let f(x) = x<sup>2</sup> + bx + c where b, c Ī R. If f(x) is a factor of both x<sup>4</sup> + 6x<sup...

Let f(x) = x2 + bx + c where b, c Ī R. If f(x) is a factor of both x4 + 6x2+ 25 and 3x4 + 4x2 +28x +5 then the least value of f(x) is

A

2

B

3

C

5/2

D

4

Answer

4

Explanation

Solution

f(x) will also be factor of

3(x4 + 6x2 + 25) – (3x4 + 4x2 + 28x + 5)

= 14 (x2 – 2x + 5)

It means x2 – 2x + 5 & x2 + bx + c have both roots common

Hence least value of

f(x) = (x – 1)2 + 4 ³ 4