(COS15度+SIN15度)X(COS15度-SIN15度)等于多少

请帮我解答下啊
请帮我写下具体步骤谢谢

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cos30度毁运并纤迹悄昌

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= cos15*cos15 - sin15*sin15 = cos(15+15)=cos30

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(cosA)^2-(sinA)^2=cos2A
原式=√3/2

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根号3除以2

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