视频 BV1kS4y1Y7EB 解析
有
cos∠BAC=-1/9
即
BC
=√(3²+1²-2·3·1·(-1/9)）
=4√6/3
且
AD为角分线
即
BD/CD
=AB/AC
=3
即
BD=√6
CD=√6/3
即
AD
=√(AB·AC-BD·CD)
=√(3·1-√6·√6/3)
=1
有
cos∠BAC=-1/9
即
BC
=√(3²+1²-2·3·1·(-1/9)）
=4√6/3
且
AD为角分线
即
BD/CD
=AB/AC
=3
即
BD=√6
CD=√6/3
即
AD
=√(AB·AC-BD·CD)
=√(3·1-√6·√6/3)
=1
