(1)52°20′+39°58′21″
=91°+78‘+21“
=92°18‘21“
(2) 180°-51°18′36″
=179°59′60″-51°18′36″
=128°41′24″
(3)25°36′47″×7
=175°+252’+329”
=179°17‘29”
(4)41°36′÷3
=39°156’÷3
=13°52’