Solution to 2001 Problem 12

We can solve this using the mirror equation or by just remembering that the image of an object placed in front of the focal point of a concave mirror is behind the mirror. The mirror equation
states that
\begin{align*}\frac{1}{d_o} + \frac{1}{d_i} = \frac{1}{f}\end{align*}
where d_o, d_i, and f are positive if and only if the object, image, and focal point (respectively) are on the reflecting side of the mirror. In our case f is positive and d_o is positive and d_o < f. Therefore,
\begin{align*}\frac{1}{d_i} = \frac{1}{f} - \frac{1}{d_o} < 0\end{align*}
Therefore, the image is not on the reflecting side of the mirror. Therefore, answer (E) is correct.

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