Let 𝑓(π‘₯) be a continuous function from ℝ to ℝ such that 𝑓(π‘₯) = 1 βˆ’ 𝑓(2 βˆ’β€¦

2024

Let 𝑓(π‘₯) be a continuous function from ℝ to ℝ such that

                𝑓(π‘₯) = 1 βˆ’ 𝑓(2 βˆ’ π‘₯)

Which one of the following options is the CORRECT value of \(∫_0^2 𝑓(π‘₯)𝑑π‘₯\)?

  1. A.

    0

  2. B.

    1

  3. C.

    2

  4. D.

    βˆ’1

Attempted by 45 students.

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Correct answer: B

Key property: f(x) + f(2 βˆ’ x) = 1 for all real x.

Let I = ∫_0^2 f(x) dx.

Integrate the given relation over [0,2]: ∫_0^2 f(x) dx + ∫_0^2 f(2 βˆ’ x) dx = ∫_0^2 1 dx = 2.

Change variables in the second integral with u = 2 βˆ’ x. Then ∫_0^2 f(2 βˆ’ x) dx = ∫_2^0 f(u) (βˆ’du) = ∫_0^2 f(u) du = I.

  • Therefore I + I = 2, so 2I = 2 and I = 1.

Conclusion: ∫_0^2 f(x) dx = 1.

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