sinb=sina*cos(a+b)……(1)=sina*cos(a+b)-cosa*sin(a+b)+cosa*sin(a+b)=-sinb+cosa*sin(a+b)∴2sinb=cosa*sin(a+b)……(2) (1)+(2):3sinb=sina*cos(a+b)+cosa*sin(a+b)=sin(2a+b)≤1∴sinb最大值为1/3===>cosb=2√2...