1981 AHSME Problems/Problem 17

The function $f$ is not defined for $x=0$, but, for all non-zero real numbers $x$, $f(x)+f\left(\dfrac{1}x\right)=x$. The equation $f(x)=f(-x)$ is satisfied by

$\textbf{(A)}\ \text{exactly one real number}

\qquad \textbf{(B)}\ \text{exactly two real numbers}

\qquad\textbf{(C)}\ \text{no real numbers}\qquad \\

\textbf{(D)}\ \text{infinitely many, but not all, non-zero real numbers}

\qquad\textbf{(E)}\ \text{all non-zero real numbers}$ (Error compiling LaTeX. ! Missing $ inserted.)

Solution

Substitute $x$ with $\frac{1}{x}$.

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

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