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Quadratic Equation and Inequalities question

2012 · Shift 0 · Q42
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  5. /2012 · Shift 0 · Q42

Quadratic Equation and Inequalities question

2012 · Shift 0 · Q42

JEE MainMathematicsQuadratic Equation and InequalitiesMCQ+4 / −1
The equation esin⁡x−e−sin⁡x−4=0{e^{\sin x}} - {e^{ - \sin x}} - 4 = 0esinx−e−sinx−4=0 has:
  1. A
    infinite number of real roots
  2. B
    no real roots
  3. C
    exactly one real root
  4. D
    exactly four real roots
View written solutionFree

Correct answer: B

  1. Start with the given equation: esin⁡x−e−sin⁡x−4=0e^{\sin x} - e^{-\sin x} - 4 = 0esinx−e−sinx−4=0 Rearranging, esin⁡x−e−sin⁡x=4e^{\sin x} - e^{-\sin x} = 4esinx−e−sinx=4

  2. Let t=sin⁡xt = \sin xt=sinx Since xxx is real, we know −1≤t≤1-1 \le t \le 1−1≤t≤1

    So the equation becomes et−e−t=4e^t - e^{-t} = 4et−e−t=4

  3. Define f(t)=et−e−t=2sinh⁡tf(t) = e^t - e^{-t} = 2\sinh tf(t)=et−e−t=2sinht We now check the possible values of f(t)f(t)f(t) for t∈[−1,1]t \in [-1,1]t∈[−1,1].

  4. Since f(t)f(t)f(t) is increasing, its maximum on [−1,1][-1,1][−1,1] occurs at t=1t=1t=1: f(1)=e−e−1f(1) = e - e^{-1}f(1)=e−e−1 Numerically, e−e−1≈2.718−0.368=2.350e - e^{-1} \approx 2.718 - 0.368 = 2.350e−e−1≈2.718−0.368=2.350

    Its minimum occurs at t=−1t=-1t=−1: f(−1)=e−1−e=−2.350f(-1) = e^{-1} - e = -2.350f(−1)=e−1−e=−2.350

    Hence, f(t)∈[−(e−e−1), e−e−1]≈[−2.350,2.350]f(t) \in [-(e-e^{-1}),\, e-e^{-1}] \approx [-2.350, 2.350]f(t)∈[−(e−e−1),e−e−1]≈[−2.350,2.350]

  5. But the equation requires f(t)=4f(t)=4f(t)=4 which is impossible because 444 is outside the range of f(t)f(t)f(t).

  6. Therefore, there is no real value of t=sin⁡xt=\sin xt=sinx satisfying the equation, and hence no real xxx satisfies it.

  7. So the equation has: no real roots\boxed{\text{no real roots}}no real roots​

  8. Comparing with the stored correct answer: Stored answer = B

    Our derived answer is also B, so they agree.

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