Value at x=5....

Question

Q: If f(x)= 1/(1+x), then find the value of f ,at x=5:

A. 21/27
B. 21/39
C. 15/39
D. 15/27
E. None

souvonik2k · Answer

f(5) = 1/6
f{f(5)} =  \frac{1}{(1+{1/6})}  =  \frac{6}{7} 
f  =  \frac{1}{(1+{6/7})}  =  \frac{7}{13} .
Checking the answer choices and reducing to lowest terms,
Answer B.

Princ · Answer

OA: B

f(x)=\frac{1}{1+x}

f(5)=\frac{1}{1+5}=\frac{1}{6}

f(\frac{1}{6})=\frac{1}{1+\frac{1}{6}}=\frac{6}{7}

f(\frac{6}{7})=\frac{1}{1+\frac{6}{7}}=\frac{7}{13}

f ,  at  x=5  is  \frac{7}{13}  or  \frac{21}{39}

Bismarck · Answer

OA:B

f(x) =\frac{1}{1+x} 
f{f(x)} =\frac{1}{1+\frac{1}{1+x}}=\frac{x+1}{x+1+1}=\frac{x+1}{x+2} 
f  =\frac{1}{1+\frac{x+1}{x+2}}=\frac{x+2}{x+2+x+1}=\frac{x+2}{2x+3}

f  =\frac{5+2}{2*5+3}=\frac{7}{13}

Multiplying denominator and numerator by  3  , we get

f  =\frac{7*3}{13*3}=\frac{21}{39}

v12345 · Answer

This type of questions are tricky one, after finding answer for 
f  = 7/13

At first instant, not finding the exact answer in answer choices, one is tempted to mark choice E, i.e. None, but as answer choices are tricky, one has to convert them to simplest form to find exact answer. 
i.e. choice (B) = 21/39 = 7/13

Posted from my mobile device

Turkish · Answer

One has to be careful. We should always reduce the numerator & the denominator if it allows. I got the answer 7/13 and went with E

Value at x=5....

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