解：?$ 300\ \mathrm {m/s}=18\ \mathrm {km/}\mathrm {\mathrm {min}}$?
?$ 400\ \mathrm {m/s}=24\ \mathrm {km/}\mathrm {\mathrm {min}}$?
?$ $?設(shè)從下午?$2 $?：?$ 00$?開始，經(jīng)過?$t_{ \mathrm {\mathrm {min}}}$?后，兩架飛機(jī)相距?$360\ \mathrm {km}$?
?$ [24(20-t)]^2+ ( 18t )^2 = 360^2$?
?$ $?解得?$t_{1}= 5.6，$??$ t_{2}= 20$?
答：在下午?$2$?時(shí)?$5$?分?$36$?秒或?$2$?時(shí)?$20$?分的時(shí)候，兩架飛機(jī)相距?$360\ \mathrm {km}。$?
