6y04a
幼苗
共回答了18个问题采纳率:94.4% 举报
|a-b|^2=[cos(α-20°)-cos(α+40°) ]^2 + [sin(α-20°)-sin(α+40°)]^2
=[cos(α-20°)]^2+[cos(α+40°)]^2-2cos(α-20°)*cos(α+40°)+[sin(α-20°)]^2+[sin(α+40°)]^2-2sin(α-20°)*sin(α+40°)
={[cos(α-20°)]^2+[sin(α-20°)]^2}+{[cos(α+40°)]^2+[sin(α+40°)]^2} -
2[cos(α-20°)*cos(α+40°)+sin(α-20°)*sin(α+40°]
=1+1-2cos[(α-20°)-(α+40°)]
=2-2cos(-60°)
=1
==>|a-b|=1
其中a^2表示a的平方
1年前
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