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Question
If f(9) = 9, f'(9) = 4, then limx9f(x)3x3 equals 
Options:
A .  2
B .  4
C .  6
D .  0
Answer: Option B
:
B
Given that f(9) = 9, f’(9) = 4
limx9f(x)3x3
On rationalisation we get -
=limx9(f(x)3x3)(x+3x+3)(f(x)+3f(x)+3)
=limx9f(x)f(9)x9 .66
=limx9f(x)f(9)x9
=f(9)
=4

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