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Let f(x) be a quadratic expression such ...

Let `f(x)` be a quadratic expression such that `f(-1)+f(2)=0`. If one root of `f(x)=0` is `3`, then the other root of `f(x)=0` lies in (A) `(-oo,-3)` (B) `(-3,oo)` (C) `(0,5)` (D) `(5,oo)`

A

`(-oo,-3)`

B

`(-3,oo)`

C

`(0,5)`

D

`(5,oo)`

Text Solution

Verified by Experts

The correct Answer is:
B
`(b)` Since one root is `3`, let
`f(x)=(x-3)(ax+b)`
`implies f(x)=ax^(2)+(b-3a)x-3b`……….`(1)`
Given, `f(-1)+f(2)=0`
`implies (a+(3a-b)-3b)+(4a+2b-6a-3b)=0`
`implies 2a-5b=0`
`implies (b)/(a)=(2)/(5)` ………..`(2)`
Now, product of roots `=(-3b)/(a)=-3((2)/(5))`
since one root of `f(x)=0` is `3`, the oher root `=(-2)/(5) in (-3,0)`
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