JEE Advanced · Mathematics · 22. Functions
Paragraph:
If a continuous \(f\) defined on the real line \(R\), assume positive and negative values in \(R\), then the equation \(f(x)=0\) has a root in \(R\). For example, if it is known that a continuous function \(f\) on \(R\) is positive at some point and its minimum values is negative, then the equation \(f(x)=0\) has a root in \(R\).
Consider \(f(x)=k e^x-x\) for all real \(x\), where \(k\) is real constant.Question:
For \(k>0\), the set of all values of \(k\) for which \(k e^x-x=0\) has two distinct roots, is
- A
\(\left(0, \frac{1}{e}\right)\)
- B
\(\left(\frac{1}{e}, 1\right)\)
- C
\(\left(\frac{1}{e}, \infty\right)\)
- D
\((0,1)\)
Answer & Solution
Correct Answer
(A)
\(\left(0, \frac{1}{e}\right)\)
Step-by-step Solution
Detailed explanation
For two distinct roots \(1+\ln k < 0(k>0)\)
\(\ln k < -1 \quad k < \frac{1}{e}\)
Hence, \(k \in\left(0, \frac{1}{e}\right)\)
\(\ln k < -1 \quad k < \frac{1}{e}\)
Hence, \(k \in\left(0, \frac{1}{e}\right)\)
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