作业帮帮一哈 那
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帮一哈 那
14.∵（2sinA-1）2+(cosB－1/2)^1/2 =0,
∴2sinA-1=0,(cosB－1/2)^1/2 =0,
∴sinA= 1/2 ,∠A=30°；
cosB= 1/2 ,∠B=60°．
∴∠C=90°．
∴△ABC是直角三角形．
15.则它的面积为240
设中位线长为x,得(上底+下底)/2=x
周长C=2x+(上底+下底)=80
80=2x+2x=4x
x=20
面积S=（上底+下底）*高/2=2x * 12/2=2*20*12/2=240
再问：
再问： 帮帮忙 谢谢
再答： 81.We won't let you down 82.They stopped to listen to the weather forecast 83.You'd better don't open the window 84.We will have a picnic this weekend 85.We have enough time to do homework
∴2sinA-1=0,(cosB－1/2)^1/2 =0,
∴sinA= 1/2 ,∠A=30°；
cosB= 1/2 ,∠B=60°．
∴∠C=90°．
∴△ABC是直角三角形．
15.则它的面积为240
设中位线长为x,得(上底+下底)/2=x
周长C=2x+(上底+下底)=80
80=2x+2x=4x
x=20
面积S=（上底+下底）*高/2=2x * 12/2=2*20*12/2=240
再问：
再问： 帮帮忙 谢谢
再答： 81.We won't let you down 82.They stopped to listen to the weather forecast 83.You'd better don't open the window 84.We will have a picnic this weekend 85.We have enough time to do homework