用度,分,秒表示77°42'+34°.45'= 108°18’-56°23’= 180°-（34°54‘+21°33’）=

77°42'+34°45'=77+34 °42+45'=111°87'=112°27'108°18’-56°23’= 107°78'-56°23'=107-56°78-23'=51°55'180°-（34°54‘+21°33’）=180°-（34+21°54+33‘)=180°-55°87'=179°60'-56°27'=123°33...