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BITSAT 2012
Exam
BITSAT
Year
2012
Subject
Mathematics
Chapter
Differentiation

BITSAT 2012 · Mathematics · Differentiation

Let f(x+y)=f(x) · f(y) for all x, y where f(0) ≠ 0 If f(5)=2 and f^...

Let f(x+y)=f(x)⋅f(y)f(x+y)=f(x) \cdot f(y) for all x,yx, y where f(0)≠0f(0) \neq 0 If f(5)=2f(5)=2 and f′(0)=3,f^{\prime}(0)=3, then f′(5)f^{\prime}(5) is equal to-

Options

  1. A6
  2. B0
  3. C1
  4. DNone of these

Correct answer

A. 6

Step-by-step solution

f′(5)=lim⁡h→0f(5+h)−f(5)h=lim⁡h→0f(5+h)−f(5+0)h=lim⁡h→0f(5)⋅f(h)−f(5)+f(0)h(∵f(x+y)=f(x),f(y)f^{\prime}(5)=\lim _{h \rightarrow 0} \frac{f(5+h)-f(5)}{h}=\lim _{h \rightarrow 0} \frac{f(5+h)-f(5+0)}{h}=\lim _{h \rightarrow 0} \frac{f(5) \cdot f(h)-f(5)+f(0)}{h}(\because f(x+y)=f(x), f(y) for all x,y)=(lim⁡h→0f(h)−f(0)h)⋅f(5)=f′(0)⋅f(5)=3×2=6x, y)=\left(\lim _{h \rightarrow 0} \frac{f(h)-f(0)}{h}\right) \cdot f(5)=f^{\prime}(0) \cdot f(5)=3 \times 2=6
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