cos(pai-a)=-1/7,cos(a+b)= - 知识问答

cos(pai-a)=-1/7,cos(a+b)=-11/14,求b

1个回答

cos(pai-a)=-1/7
cos(a)=1/7 sin(a)=4√3/7
cos(a+b)=-11/14
cos(a+b)=cos(a)cos(b)-sin(a)sin(b)=-11/14
cos(b)/7-4√3sin(b)/7=-11/14
cos(b)=4√3sin(b)-11/2
sin(b)平方+cos(b)平方=1
sin(b)=√3/2
b=60

相关问题