Question 1143861
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In this problem the words related to the light bulb and to the focus are all  IRRELEVANT.


The correct formulation after editing, &nbsp;removing all unnecessary words, &nbsp;is <U>THIS</U> :



<pre>
    A parabolic reflector has the opening of 18 inches in diameter and is 10 inches deep. 
    What is an equation of the parabola in the parabolic reflector?
</pre>


The rest of the words in the original formulation are only to make an obstacle for a reader 
to quick and correct understanding the problem.