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

Suppose a differentiable function \(f ( x )\) satisfies the identity \(f(x+y)=f(x)+f(y)+x y^{2}+x^{2} y\) for all real \(x\) and \(y .\) If \(\lim \limits_{x \rightarrow 0} \frac{f(x)}{x}=1,\) then \(f^{\prime}(3)\) is equal to 

  1. A \(8\)
  2. B \(9\)
  3. C \(10\)
  4. D \(12\)
Verified Solution

Answer & Solution

Correct Answer

(C) \(10\)

Step-by-step Solution

Detailed explanation

since, \(\lim _{x \rightarrow 0} \frac{f(x)}{x}\) exist \(\Rightarrow f(0)=0\) Now, \(f^{\prime}(x)=\lim _{h \rightarrow 0} \frac{f(x+h)-f(x)}{h}\) \(=\lim _{h \rightarrow 0} \frac{f(h)+x h^{2}+x^{2} h}{h}(\operatorname{tak}(y=h)\)…
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