Difference between revisions of "1953 AHSME Problems/Problem 35"

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==Solution==
 
==Solution==
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First simplify <math>f(x+2)</math>:
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<cmath>f(x+2)=\frac{(x+2)(x+1)}{2}.</cmath>
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Then simplify the answers and see which one matches.
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<math>f(x)+f(2)=\frac{x(x-1)}{2} + 1,</math>
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<math>(x+2)f(x)=\frac{(x+2)x(x-1)}{2},</math>
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<math>x(x+2)f(x)=\frac{(x+2)x^2(x-1)}{2},</math>
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<math>\frac{xf(x)}{x+2}=\frac{x^2(x-1)}{2(x+2)},</math>
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<math>\frac{(x+2)f(x+1)}{x}=\frac{(x+2)(x+1)}{2}.</math>
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Since <math>f(x+2)=\frac{(x+2)f(x+1)}{x}=\frac{(x+2)(x+1)}{2}</math>, the answer is <math>\boxed{\textbf{(E)}\ \frac{(x+2)f(x+1)}{x}}.</math>
  
 
==See Also==
 
==See Also==

Revision as of 20:32, 24 January 2020

Problem

If $f(x)=\frac{x(x-1)}{2}$, then $f(x+2)$ equals:

$\textbf{(A)}\ f(x)+f(2) \qquad \textbf{(B)}\ (x+2)f(x) \qquad \textbf{(C)}\ x(x+2)f(x) \qquad \textbf{(D)}\ \frac{xf(x)}{x+2}\\ \textbf{(E)}\ \frac{(x+2)f(x+1)}{x}$

Solution

First simplify $f(x+2)$: \[f(x+2)=\frac{(x+2)(x+1)}{2}.\] Then simplify the answers and see which one matches.

$f(x)+f(2)=\frac{x(x-1)}{2} + 1,$

$(x+2)f(x)=\frac{(x+2)x(x-1)}{2},$

$x(x+2)f(x)=\frac{(x+2)x^2(x-1)}{2},$

$\frac{xf(x)}{x+2}=\frac{x^2(x-1)}{2(x+2)},$

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

Since $f(x+2)=\frac{(x+2)f(x+1)}{x}=\frac{(x+2)(x+1)}{2}$, the answer is $\boxed{\textbf{(E)}\ \frac{(x+2)f(x+1)}{x}}.$

See Also

1953 AHSC (ProblemsAnswer KeyResources)
Preceded by
Problem 13
Followed by
Problem 15
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All AHSME Problems and Solutions


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