(cosπ/12-sinπ/12)(cosπ/12+sinπ/12)的值为

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(cosπ/12-sinπ/12)(cosπ/12+sinπ/12)的值为
(cosπ/12-sinπ/12)(cosπ/12+sinπ/12)的值为

(cosπ/12-sinπ/12)(cosπ/12+sinπ/12)的值为
由(cosπ/12-sinπ/12)(cosπ/12+sinπ/12)=cos^2(π/12)-sin^2(π/12)=cosπ/6=cos30=sin60=根号3/2 cos2a=cos^2a-sin^2a

cos^2(π/12)-sin^2(π/12)=cosπ/6
平方差公式和倍角的余弦公式结合