CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2001

  • question_answer
    If \[f(x+y)=f(x).f(y),f(3)=3,\]\[f(0)=11\]then\[f(3)\]is equal to:

    A)  \[11.{{e}^{33}}\]                             

    B)  33

    C)  11                         

    D)         log 33

    E)  none of these

    Correct Answer: B

    Solution :

    \[f(3)=\underset{h\to 0}{\mathop{\lim }}\,\frac{f(3+h)-f(3)}{h}\] \[=\underset{h\to 0}{\mathop{\lim }}\,\frac{f(3)f(h)-f(3)}{h}\]                                 \[(\because f(x+y)=f(x)f(y))\] Now, \[f(x+0)=f(x)f(0)\] \[\Rightarrow \]               \[f(x)[f(0)-1]=0\] Either\[f(x)=0\]or\[f(0)=1\] \[\therefore \]  \[f(3)=f(3)\underset{h\to 0}{\mathop{\lim }}\,\frac{F(h)-f(0)}{h}\]                 \[=f(3)f(0)=f(3).11\]                 \[=3\times 11=33\]


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