=cos21°+cos289°+…+cos244°+cos246°+cos245°
=（cos21°+cos289°）+…+（cos244°+cos246°）+（
| ||
| 2 |
=
| ||
| 44個(gè)1 |
| 1 |
| 2 |
=44
| 1 |
| 2 |
化簡(jiǎn)：cos21°+cos22°+cos23°+…+cos289°．
化簡(jiǎn)：cos21°+cos22°+cos23°+…+cos289°．
數(shù)學(xué)人氣：675 ℃時(shí)間：2020-01-29 20:24:15
優(yōu)質(zhì)解答
cos21°+cos22°+cos23°+…+cos289°
=cos21°+cos289°+…+cos244°+cos246°+cos245°
=（cos21°+cos289°）+…+（cos244°+cos246°）+（
）2
=
+
=44
．
=cos21°+cos289°+…+cos244°+cos246°+cos245°
=（cos21°+cos289°）+…+（cos244°+cos246°）+（
=
=44
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