$解：最遠點在?F?到圓?O?的切線的切點，即點?Q?$
$∵?FQ?與圓?O?相切，?∠FQO=90°?$
$?PF=350\ \mathrm {km}，??PO=OQ=6400\ \mathrm {km}，??FO=6400+350=6750\ \mathrm {km}?$
$∴?cosα=\frac {OQ}{OF}=\frac {6400}{6750}?$
$∴?α≈18.53° \frac {α}2≈9.27°?$
$∴?PQ=2×6400×sin {\frac {α}2}≈2061.0\ \mathrm {km}?$
