1.解:“新闻联播“节目,钟表上时针与分针所成的最小的角的度数为30°×5=150°.”新闻30分“节目,钟表上时针与分针所成的最小的角的度数为0°.
2.解:如图16所示.
3. 解:(1) 30°19'21"+15°40'42”=45°59'63"=46°3".
(2)90°-68°17'50"=89°59'60"- 68°17'50"= 21°42'10".
(3)40 49 12
(4)52°22'X9=52°X9+22'X9=468°+198′=471°18'.
(5)178°53'÷5 =175°233'÷5=35°46. 6'≈35°47'.
4.解:当射线OC在∠AOB内部时,如图17 (1)所示,∠AOC=∠AOB-∠BOC=72°-36°=36°.当射线OC在∠AOB外部时,如图17 (2)所示,∠AOC=∠AOB+∠BOC=72°+36°=108°.