If cos 330deg=sqrt3/2 show how to calculate two possible answers for cos165deg (without using a calculator)?
回答 (1)
2016-12-05 6:46 pm
cos²(330/2) = (1+cos(330))/2
= (1+√3/2)/2
= (2+√3)/4
cos(330/2) = ±√((2+√3)/4) = ± √(2+√3) / 2
= (1+√3/2)/2
= (2+√3)/4
cos(330/2) = ±√((2+√3)/4) = ± √(2+√3) / 2
收錄日期: 2021-04-23 23:58:16
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