己知tana=3求:(1)sina+2cosa/5cosa-sina (2)1/2sina*cosa+cos2a (3)sina*cosa
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解决时间 2021-03-20 08:21
- 提问者网友：雾里闻花香
- 2021-03-19 19:11
己知tana=3求:(1)sina+2cosa/5cosa-sina (2)1/2sina*cosa+cos2a (3)sina*cosa
最佳答案
- 五星知识达人网友：举杯邀酒敬孤独
- 2021-03-19 20:45
解1(sina+2cosa)×1/(cosa)/(5cosa-sina)×(1/cosa)
=(tana+2)/(5-tana)
=(3+2)/(5-3)
=5/2
2 1/2sina*cosa+cos2a
=(cos^2a+sin^2a)/(2sinacosa+cos^2a-sin^2a)
=(cos^2a+sin^2a)×(1/cos^2a)/(2sinacosa+cos^2a-sin^2a)×(1/cos^2a)
=(1+tan^2a)/(2tana+1-tan^2a)
=(1+3^2)/(2×3+1-3^2)
=10/(-2)
=-5
sina*cosa
=sina*cosa/(sin^2a+cos^2a)
=tana/(1+tan^2a)
=3/10
=(tana+2)/(5-tana)
=(3+2)/(5-3)
=5/2
2 1/2sina*cosa+cos2a
=(cos^2a+sin^2a)/(2sinacosa+cos^2a-sin^2a)
=(cos^2a+sin^2a)×(1/cos^2a)/(2sinacosa+cos^2a-sin^2a)×(1/cos^2a)
=(1+tan^2a)/(2tana+1-tan^2a)
=(1+3^2)/(2×3+1-3^2)
=10/(-2)
=-5
sina*cosa
=sina*cosa/(sin^2a+cos^2a)
=tana/(1+tan^2a)
=3/10
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