cosπ/4+cos2π/4+cos3π/4+cos4π/4=
√2/2+0+(-√2/2)+(-1) --->唔明呢個step!
=-1
可以解釋下嗎?
cosπ/4+cos2π/4+cos3π/4+cos4π/4=?
2007-09-30 6:24 pm
回答 (2)
2007-09-30 6:49 pm
✔ 最佳答案
[ As π/4 is a special angle, cosπ/4 = √2/2 <--- you can find that in your bookcos3π/4 = cos(π - π/4) = - cosπ/4 = (-√2/2) < --- since cos(π - angle) = -cos (angle)]
so, cosπ/4+cos2π/4+cos3π/4+cos4π/4
=√2/2+0+(-√2/2)+(-1)
= 0 + 0 -1
= -1
2007-10-01 2:16 am
用計算機la你~~~~~~
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原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20070930000051KK01075