MCQMediumJEE 2023Functions

JEE Mathematics 2023 Question with Solution

Let f:RRf : \mathbb{R} \to \mathbb{R} be a function such that

f(x)=x2+2x+1x+1f(x) = \frac{x^2 + 2x + 1}{x + 1}
  • A

    f(x)f(x) is many-one in (,1)(-\infty, -1)

  • B

    f(x)f(x) is many-one in (1,)(1, \infty)

  • C

    f(x)f(x) is one-one in [1,)[1, \infty) but not in (,)(-\infty, \infty)](streamdown:incomplete-link)

  • D

    f(x)f(x) is one-one in (,)(-\infty, \infty)

Answer

Correct answer:B

Step-by-step solution

Standard Method

Given:

f(x)=x2+2x+1x+1f(x) = \frac{x^2 + 2x + 1}{x + 1}

Find: Whether f(x)f(x) is one-one or many-one on the stated intervals.

The solution rewrites and analyzes a different function:

f(x)=x2+2x+1x2+1f(x) = \frac{x^2 + 2x + 1}{x^2 + 1}

and concludes that the correct option is B. Since the solution conclusion is the primary source, the extracted answer is B.

Also, from the given question expression itself,

x2+2x+1=(x+1)2x^2 + 2x + 1 = (x+1)^2

so for x1x \neq -1,

f(x)=(x+1)2x+1=x+1f(x) = \frac{(x+1)^2}{x+1} = x+1

This shows the given question text and the provided the solution are inconsistent with each other. The answer has therefore been taken from the solution as instructed, despite this discrepancy.

Discrepancy Note

Given: The question states

f(x)=x2+2x+1x+1f(x) = \frac{x^2 + 2x + 1}{x + 1}

while the solution works with

f(x)=x2+2x+1x2+1=1+2xx2+1f(x) = \frac{x^2 + 2x + 1}{x^2 + 1} = 1 + \frac{2x}{x^2 + 1}

Find: Which source determines the answer.

The solution explicitly says The Correct Option is B and its working is based on the denominator x2+1x^2+1, not x+1x+1. Therefore, these provided inputs refer to mismatched statements. Under the, the solution is treated as authoritative for the answer, so the recorded answer is B.

The source mismatch should be reviewed manually.

Common mistakes

  • Using the answer key without checking the solution. Here the two sources disagree, and the extraction rule gives priority to the solution.

  • Assuming the worked differentiation applies to the displayed question. The solution differentiates a different function with denominator x2+1x^2+1, so that reasoning cannot be transferred directly to the shown question.

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