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JEE Mains · Maths · STD 12 - 5. continuity and differentiation

Let \(f\) be a twice differentiable function defined on \(R\) such that \(f (0)=1, f ^{\prime}(0)=2\) and \(f ^{\prime}( x ) \neq 0\) for all \(x \in R\). If \(\left|\begin{array}{ll}f(x) & f^{\prime}(x) \\ f^{\prime}(x) & f^{\prime \prime}(x)\end{array}\right|=0,\) for all \(x \in R,\) then the value of \(f (1)\) lies in the interval:

  1. A \((9,12)\)
  2. B \((6,9)\)
  3. C \((0,3)\)
  4. D \((3,6)\)
Verified Solution

Answer & Solution

Correct Answer

(B) \((6,9)\)

Step-by-step Solution

Detailed explanation

\(f ( x ) f ^{\prime \prime}( x )-\left( f ^{\prime}( x )\right)^{2}=0\) \(\frac{ f ^{\prime \prime}( x )}{ f ^{\prime}( x )}=\frac{ f ^{\prime}( x )}{ f ( x )}\) \(\ln \left( f ^{\prime}( x )\right)=\ln f ( x )+\ln c\) \(f ^{\prime}( x )=\operatorname{cf}( x )\)…
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