daking2006
幼苗
共回答了21个问题采纳率:95.2% 举报
① ∵ sin a = m
∴ sin (3 π - a)
= sin(2 π - π + a)
= sin(- π + a)
= - sin(π - a)
= - sin a
= - m
② √(1 - cos ² 1200°)
= √(sin ² 1200° + cos ² 1200° - cos ² 1200°)
= √(sin ² 1200°)
= 丨sin 1200°丨
= 丨sin (360° × 3 + 120°)丨
= 丨sin 120° 丨
= 丨sin(180 ° - 60°)丨
= 丨sin 60°丨
= 丨√3 / 2丨
= √3 / 2
1年前
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