cosα+sinα不等于 A.√2cos[α-(π

1个回答

很显然是C,没有系数√2
cosα+sinα=√2 (cos45°cosα+sin45°sinα)=√2cos[α-(π/4)] A正确,cosα=cos(-α),所以B正确
cosα周期是2π,所以√2cos[α-(π/4)] =√2cos[α-(π/4)+2π] =√2cos[α+(7π/4)] D正确

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