sina = 2cosa ï¼tana = 2ï¼
(cosa)^2 = 1 / [1 + (tana)^2] = 1/5 ï¼(sina)^2 = 4/5 ã
1ãå¦æ a æ¯ç¬¬ä¸è±¡éè§ï¼å sina = 2â5/5ï¼cosa = â5/5ï¼
2ãå¦æ a æ¯ç¬¬ä¸è±¡éè§ï¼å sina = -2â5/5ï¼cosa = -â5/5 ã
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