\frac{1}{k} = \frac{1}{f} - \frac{1}{a}

${\frac{1}{k} = \frac{1}{f} - \frac{1}{a}}$

\frac{1}{k} = \frac{1}{f} - \frac{1}{a}

$\frac{1}{k} = \frac{1}{f} - \frac{1}{a}$

\frac{1}{k}

$\frac{1}{k}$

f

$f$

f

$f$

1

a

$a$

1

Lisa

OK

Error