Question 1208434
<pre>
{{{1/f}}}{{{""=""}}}{{{(n - 1)(1/a + 1/b)}}}

Invert both sides:

{{{f/1}}}{{{""=""}}}{{{1^""/((n - 1)(1/a + 1/b))}}}

Multiply top and bottom by ab:

{{{f}}}{{{""=""}}}{{{ab/((n - 1)(b + a))}}}

Edwin</pre>