2cos²a+3cosa.sina-3sin²a/sin²a+cos²a为什么等于2+3tana-3tan²a/1+tan²a?
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![2cos²a+3cosa.sina-3sin²a/sin²a+cos²a为什么等于2+3tana-3tan²a/1+tan²a?](/uploads/image/z/3712541-5-1.jpg?t=2cos%26%23178%3Ba%2B3cosa.sina-3sin%26%23178%3Ba%2Fsin%26%23178%3Ba%2Bcos%26%23178%3Ba%E4%B8%BA%E4%BB%80%E4%B9%88%E7%AD%89%E4%BA%8E2%2B3tana-3tan%26%23178%3Ba%2F1%2Btan%26%23178%3Ba%3F)
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2cos²a+3cosa.sina-3sin²a/sin²a+cos²a为什么等于2+3tana-3tan²a/1+tan²a?
2cos²a+3cosa.sina-3sin²a/sin²a+cos²a为什么等于2+3tana-3tan²a/1+tan²a?
2cos²a+3cosa.sina-3sin²a/sin²a+cos²a为什么等于2+3tana-3tan²a/1+tan²a?
(2cos²a+3cosa*sina-3sin²a)/(sin²a+cos²a) (分子分母同除以cos²a即得)
=(2+ 3sina/cosa - 3sin²a/cos²a)/(sin²a/cos²a +1)
=(2+3tana -3tan²a)/(tan²a +1)