我来帮你;
cos(π/5+2)cos(π/5-2)展开处理:
(cosπ/5cos2-sinπ/5sin2)(cosπ/5cos2+sinπ/5sin2)=(cosπ/5cos2)^2-(sinπ/5sin2)^2
=(cos(π/5)+sin2)(cosπ/5-sin2)=cos^2(π/5)-sin^2;
对照答案选项,发现和C吻合.因此本题选择C.
回答完毕!但愿对你有帮助!祝你学习进步!
我来帮你;
cos(π/5+2)cos(π/5-2)展开处理:
(cosπ/5cos2-sinπ/5sin2)(cosπ/5cos2+sinπ/5sin2)=(cosπ/5cos2)^2-(sinπ/5sin2)^2
=(cos(π/5)+sin2)(cosπ/5-sin2)=cos^2(π/5)-sin^2;
对照答案选项,发现和C吻合.因此本题选择C.
回答完毕!但愿对你有帮助!祝你学习进步!