|sin(a+b)|小于等于|sina|+|sinb|的证明,
问题描述：
|sin(a+b)|小于等于|sina|+|sinb|的证明,
答
|sin(a+b)|=Isinacosb+cosasinbI
≤IsinacosbI+IsinbcosaI
∵IcosaI≤1 IcosbI≤1
∴|sin(a+b)|≤IsinaI+IsinbI