How can I further simplify the following equation:

AC =      BC²
        __________
          _________
         ?BD²-BC²
 

I'm guessing that AC, BD and BC are simple variables instead of "A times C" so I don't think you can get something simpler. There's no way to remove any of those members or remove operators only with that if there's no relation between them, maybe if it's something derived from a geometry problem you can find another way to reach the same result, but you'll need more data.

I thought so. Actually

  _______
?BD²-BC²

Is derived from the Pythagorean theorem, once a side of a rectangle triangle is obtained as a denominator in the equivalence of the tangent of two similar triangles.