Question 256884
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Note that 5 divided by 1.25 is 4.  Hence the LCD is 5<i>f</i>.

*[tex \LARGE \ \ \ \ \ \ \ \ \ \ \frac{1}{f}\ +\ \frac{1}{1.25f}\ =\ \frac{1}{5}]

*[tex \LARGE \ \ \ \ \ \ \ \ \ \ \frac{1}{f}\left(\frac{5}{5}\right)\ +\ \frac{1}{1.25f}\left(\frac{4}{4}\right)\ =\ \frac{1}{5}\left(\frac{f}{f}\right)]

*[tex \LARGE \ \ \ \ \ \ \ \ \ \ \frac{5}{5f}\ +\ \frac{4}{5f}\ =\ \frac{f}{5f}]

You can take it from here, I think.

John
*[tex \LARGE e^{i\pi} + 1 = 0]
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