(1)sin20° sin35° sin70° sin82°;
(2)cos12° cos28° cos45° cos89°;
(3)tan5°tan32° tan55° tan80°;
(1)sin 54°,(2)cos 40°,(3)tan 38°,(4)sin17°54′,(5)cos57°32′58″,
(6)tan 73°20″,(7)sin28.7°﹣cos54°36′+tan51°47′,(8)tan 24.5°•tan 65.5°.
请你写出一个能分解的二次四项式并把它分解 .
①sin30° 2sin15°cos15°;
②sin36° 2sin18°cos18°;
③sin45° 2sin22.5°cos22.5°;
④sin60° 2sin30°cos30°;
⑤sin80° 2sin40°cos40°.
猜想:已知0°<α<45°,则sin2α 2sinαcosα.
(1)已知sinα=0.4771,求∠α;
(2)已知cosα=0.8451,求∠α;
(3)已知tanα=1.4106,求∠α.
(1)sin71°24′
(2)cos54°21′18″
(3)tan21°17′23″.