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TS EAMCET · Maths · Application of Derivatives

Let \(f(x)=e^x \cos x+1\). Which of the following statements is always true?

  1. A Between any two consecutive roots of \(f(x)=0\) there is always a root of \(e^x \sin x+1=0\)
  2. B Between any two consecutive roots of \(f(x)=0\) there is always a root of \(e^x \sin x-1=0\)
  3. C Between any two consecutive roots of \(f(x)=0\) there is always a root of \(e^x \cos x=0\)
  4. D Between any two consecutive roots of \(f(x)=0\) there is always a roots of \(e^x \sin x=0\)
Verified Solution

Answer & Solution

Correct Answer

(D) Between any two consecutive roots of \(f(x)=0\) there is always a roots of \(e^x \sin x=0\)

Step-by-step Solution

Detailed explanation

Let \(f(x)=\cos x+e^{-x}\) and \(\alpha\) and \(\beta\) be two roots of the question \(e^x \cos x+1=0\) such that \(\alpha < \beta\), then \(\cos \alpha+e^{-\alpha}=0\) and \(\cos \beta+e^{-\beta}=0\) clearly, \(f(x)\) is continous on \([\alpha, \beta]\) and differentiable on…
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