✔ 最佳答案
(1)
sin150° + cos240°
= sin(180° - 30°) + cos(180° + 60°)
= sin30° - cos60°
= (1/2) - (1/2)
= 1
=====
(2)
sin300° - cos330°
= sin(360° - 60°) - cos(360° -30°)
= -sin60° - cos60°
= -(√3/2) - (√3/2)
= -√3
=====
(3)
sin225° / (1 - cos300°)
= sin(180°+ 45°) / [1 - cos(360° -60°)]
= -sin45° / [1 - cos60°]
= -(√2/2)] / [1 - (1/2)]
= -(√2)/2) / [(1/2)]
= -√2
=====
(4)
Case 1 :
tan225° + [sin210° / tan²330°]
= tan(180°+ 45°) + [sin(180°+ 30°) / tan²(360° - 30°)]
= tan45° + [(-sin30°) / tan²30°]
= 1 + [(-1/2) / (1/√3)²]
= 1 + [(-1/2) / (1/3)]
= 1 - 3/2
= -1/2
Case 2 :
[tan225° + sin210°] / tan²330°
= [tan(180°+ 45°) + sin(180°+ 30°)] / tan²(360° - 30°)
= [tan45° - sin30°] / tan²30°
= [1 - (1/2)] / (1/√3)²
= (1/2) / (1/3)
= 3/2
=====
(5)
[sin450°cos225°] / [sin(-45°)cos315°]
= [sin(360°+ 90°)cos(180°+ 45°)] / [-sin45°cos(360°- 45°)]
= [sin90°(-cos45°)]/ [-sin45°cos45°]
= [1 × (-1/√2)] / [(-1/√2) × (1/√2)]
= √2
=====
(6)
[tan210° + tan240°] / [tan300° + sin420°]
= [tan(180° + 30°) +tan(180° + 60°)]/ [tan(360° - 60°) +sin(360° + 60°)]
= [tan30° +tan60°] / [-tan60° + sin60°]
= [(√3/3) + √3] / [-√3 + √3/2]
= (4√3/3) / (-√3/2)
= (4/3) × 2
= 8/3
2014-08-11 09:12:11 補充:
不知是打錯還是計算錯。
第一題是:
.........
= (1/2) - (1/2)
= 0 ..... (答案)