数学人才们,为什么要那么做!拍照发送的答案更关注!
来源:学生作业帮 编辑:搜狗做题网作业帮 分类:数学作业 时间:2024/06/23 13:05:19
数学人才们,为什么要那么做!拍照发送的答案更关注!
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^2-a^2-c^2/c^2-a^2-b^2=-2accosB/-2abcosC=sinCcosB/sinBcosC
sincsinbcosc=(2sina-sinc)sinccosb
sinbcosc=2sinacosb-sinccosb
sinbcosc+sinccosb=2sinacosb
sina=2sinacosb
cosb=1/2
B=60°
(2)T=1-cos2A/2+3/4+1-cos2C/2
=1+3/4-cos2A/2-COS(240°-2A)/2
=7/4-(cos2A/2-(cos2A/2-根号3/2*sin2A)/2
=7/4-COS2A/4+根号3/4*sin2A
=7/4+1/2sin(2A-30°)
1/2 >1 / 2sin(2A-30°) >-1/4
9/4 > T>3/2
sincsinbcosc=(2sina-sinc)sinccosb
sinbcosc=2sinacosb-sinccosb
sinbcosc+sinccosb=2sinacosb
sina=2sinacosb
cosb=1/2
B=60°
(2)T=1-cos2A/2+3/4+1-cos2C/2
=1+3/4-cos2A/2-COS(240°-2A)/2
=7/4-(cos2A/2-(cos2A/2-根号3/2*sin2A)/2
=7/4-COS2A/4+根号3/4*sin2A
=7/4+1/2sin(2A-30°)
1/2 >1 / 2sin(2A-30°) >-1/4
9/4 > T>3/2