为锐角三角形,
…………………………………………………………3分
(I)
,
……………6分
(II)|3 m -2 n | 2=9 m 2+4 n 2-12 m · n =13-12(sin A cos B +cos A sin B )
=13-12sin( A + B )=13-12sin(2 B +
)=13-
略
为锐角三角形,
…………………………………………………………3分
(I)
,
……………6分
(II)|3 m -2 n | 2=9 m 2+4 n 2-12 m · n =13-12(sin A cos B +cos A sin B )
=13-12sin( A + B )=13-12sin(2 B +
)=13-
略