cos(a-阝/2)=-1/9,sin(a/2-阝)=2/3,且兀/2
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![cos(a-阝/2)=-1/9,sin(a/2-阝)=2/3,且兀/2](/uploads/image/z/10157531-59-1.jpg?t=cos%28a-%E9%98%9D%2F2%29%3D-1%2F9%2Csin%28a%2F2-%E9%98%9D%29%3D2%2F3%2C%E4%B8%94%E5%85%80%2F2)
cos(a-阝/2)=-1/9,sin(a/2-阝)=2/3,且兀/2
cos(a-阝/2)=-1/9,sin(a/2-阝)=2/3,且兀/2
cos(a-阝/2)=-1/9,sin(a/2-阝)=2/3,且兀/2
你这个问题提过啊,我复制一下啊a+b=2((a-b/2)-(a/2-b)),
sin(a+b)=sin(2(a-b/2)-(a/2-b))=2sin((a-b/2)-(a/2-b))cos((a-b/2)-(a/2-b))
因为兀/2