锟斤拷锟斤拷锟节革拷锟叫旓拷锟絎锟叫ｏ拷锟叫旓拷锟街憋拷要锟絣锟斤拷锟侥凤拷锟斤拷锟斤拷锟铰ｏ拷

锟斤拷锟斤拷1.锟斤拷锟叫筹拷锟斤拷要锟紺锟斤拷锟斤拷锟斤拷锟絵锟斤拷然锟斤拷謩e锟斤拷锟斤拷锟斤拷謼l锟斤拷锟酵憋拷要锟絣锟斤拷锟組锟斤拷锟紺锟斤拷锟斤拷

锟斤拷锟斤拷2.锟斤拷锟节筹拷謼l锟斤拷锟斤拷锟揭傦拷锟斤拷要锟紺锟斤拷锟斤拷锟絣锟斤拷锟斤拷锟斤拷锟絩锟斤拷锟斤拷要锟紺锟斤拷锟斤拷锟斤拷锟絵也一锟斤拷锟斤拷锟斤拷锟斤拷

锟斤拷锟斤拷3.锟斤拷锟节憋拷要锟絣锟斤拷锟斤拷锟揭傦拷锟斤拷要锟紺锟斤拷锟斤拷锟斤拷要锟紺锟斤拷锟斤拷锟斤拷锟絵锟斤拷锟斤拷锟絩锟斤拷锟絣锟斤拷也一锟斤拷锟斤拷锟斤拷锟斤拷

锟斤拷锟斤拷4.锟斤拷锟斤拷锟街條锟斤拷锟酵憋拷要锟絣锟斤拷锟斤拷锟斤拷锟紺锟斤拷锟斤拷锟絫锟斤拷要锟紺锟斤拷锟斤拷锟斤拷锟絵锟斤拷锟斤拷锟斤拷

锟斤拷锟斤拷5.锟斤拷锟斤拷锟街條锟斤拷锟酵憋拷要锟絣锟斤拷锟斤拷锟斤拷一锟斤拷未锟斤拷锟紺锟斤拷锟斤拷锟絫锟給锟斤拷锟矫筹拷锟結論锟斤拷锟斤拷要锟紺锟斤拷锟斤拷锟斤拷锟絵未锟截筹拷锟斤拷锟斤拷

锟斤拷锟斤拷6.锟斤拷锟紺锟斤拷锟絩锟斤拷锟斤拷锟斤拷锟斤拷锟矫凤拷锟紺锟斤拷锟斤拷锟斤拷锟絎锟絯锟絳锟斤拷锟饺凤拷锟斤拷锟斤拷

锟斤拷锟斤拷7.锟节戯拷锟矫筹拷直锟揭�锟絣锟斤拷锟組锟斤拷锟紺锟斤拷锟絩锟斤拷锟斤拷要注锟斤拷l锟斤拷锟侥猴拷锟斤拷锟皆猴拷邏輯锟侥囷拷锟斤拷锟斤拷锟斤拷

锟斤拷锟斤拷锟斤拷锟斤拷锟斤拷一锟斤拷锟叫旓拷锟街憋拷要锟絣锟斤拷锟斤拷锟斤拷锟絵锟斤拷

锟斤拷锟斤拷锟斤拷知锟斤拷锟斤拷锟斤拷ABC锟斤拷锟斤拷锟斤拷∠BAC=60°锟斤拷锟斤拷锟斤拷锟斤拷锟斤拷锟斤拷ABC锟斤拷锟紺锟斤拷锟斤拷AC2=AB·BC锟侥筹拷直锟揭�锟絣锟斤拷锟斤拷∠ABC=120°锟斤拷

锟斤拷锟斤拷锟斤拷锟斤拷锟斤拷

锟斤拷锟斤拷锟斤拷锟斤拷锟斤拷锟揭傦拷锟斤拷要锟斤拷锟絖锟斤拷直锟揭�锟絣锟斤拷锟侥讹拷锟絰锟斤拷锟斤拷直锟揭�锟絣锟斤拷指锟斤拷锟斤拷A锟絣锟斤拷锟斤拷锟斤拷锟斤拷B锟絣锟斤拷锟斤拷锟斤拷锟侥筹拷謼l锟斤拷锟斤拷同锟絩B锟絣锟斤拷锟斤拷锟斤拷锟斤拷A锟絣锟斤拷锟斤拷锟斤拷锟侥憋拷要锟絣锟斤拷锟斤拷也锟斤拷锟斤拷锟絝锟斤拷锟斤拷锟紸锟絣锟斤拷锟斤拷锟斤拷锟斤拷锟絫B锟絣锟斤拷也一锟斤拷锟斤拷锟斤拷锟斤拷锟斤拷锟紹锟絣锟斤拷锟斤拷锟斤拷锟斤拷锟絫A锟絣锟斤拷也一锟斤拷锟斤拷锟斤拷锟斤拷

锟斤拷锟斤拷锟紽锟节ｏ拷锟揭傦拷锟斤拷锟斤拷一锟斤拷锟紷锟斤拷锟絵目锟斤拷要锟紺锟斤拷AC2=AB·BC锟侥筹拷直锟揭�锟絣锟斤拷锟斤拷∠ABC=120°锟斤拷锟揭傦拷锟斤拷要锟街別锟紺锟斤拷锟缴傦拷锟斤拷锟斤拷

锟斤拷锟斤拷1.锟斤拷謼l锟斤拷锟斤拷锟斤拷锟�∠ABC=120°锟斤拷锟絫AC2=AB·BC锟斤拷

锟斤拷锟斤拷锟揭傦拷锟斤拷锟斤拷通锟絕锟斤拷锟揭讹拷锟斤拷锟斤拷C锟斤拷锟紷锟斤拷锟絣锟斤拷锟斤拷锟斤拷锟斤拷锟揭讹拷锟斤拷锟斤拷知锟斤拷

锟斤拷锟斤拷AC2=AB2+BC2-2AB·BCcos∠ABC

锟斤拷锟斤拷锟斤拷∠ABC=120°锟絩锟斤拷cos∠ABC=-0.5锟斤拷锟斤拷锟斤拷锟斤拷式锟缴得ｏ拷

锟斤拷锟斤拷AC2=AB2+BC2+AB·BC

锟斤拷锟斤拷锟斤拷項后即可得碉拷AC2=AB·BC锟斤拷锟斤拷锟斤拷謼l锟斤拷锟斤拷锟斤拷锟斤拷

锟斤拷锟斤拷2.锟斤拷要锟絣锟斤拷锟斤拷锟斤拷锟紸C2=AB·BC锟斤拷锟絫∠ABC=120°锟斤拷

锟斤拷锟斤拷同锟斤拷锟斤拷锟揭傦拷锟斤拷锟斤拷使锟斤拷锟斤拷锟揭讹拷锟斤拷锟斤拷C锟斤拷锟紷锟斤拷锟絣锟斤拷锟斤拷锟斤拷锟斤拷锟揭讹拷锟斤拷锟斤拷知锟斤拷

锟斤拷锟斤拷cos∠ABC=(AB2+BC2-AC2)/2AB·BC

锟斤拷锟斤拷锟斤拷AC2=AB·BC锟絩锟斤拷锟斤拷锟斤拷锟斤拷式锟缴得ｏ拷

锟斤拷锟斤拷cos∠ABC=0.5

锟斤拷锟斤拷锟斤拷锟�∠ABC锟斤拷锟絁锟角ｏ拷锟斤拷锟斤拷cos∠ABC锟斤拷須达拷锟斤拷0锟斤拷锟斤拷锟�锟斤拷∠ABC锟斤拷須碉拷锟斤拷120°锟斤拷锟斤拷锟斤拷要锟絣锟斤拷锟斤拷锟斤拷锟斤拷

锟斤拷锟斤拷锟紺锟斤拷锟斤拷锟斤拷锟斤拷锟揭傦拷锟斤拷锟皆得筹拷锟結論锟斤拷AC2=AB·BC锟侥筹拷直锟揭�锟絣锟斤拷锟斤拷∠ABC=120°锟斤拷

锟斤拷锟斤拷锟斤拷锟絇锟斤拷锟絔锟斤拷

锟斤拷锟斤拷锟竭匡拷锟斤拷锟絎知锟絉锟絚锟絉锟斤拷

锟斤拷锟斤拷锟斤拷锟斤拷锟斤拷锟斤拷锟绞裁�

锟斤拷锟铰高匡拷锟結訊锟斤拷锟竭匡拷锟斤拷锟竭★拷锟斤拷前锟绞傦拷锟斤拷志愿锟斤拷锟斤拷取锟街旓拷锟斤拷锟斤拷

锟竭匡拷锟絩锟絞锟斤拷锟斤拷全锟斤拷锟斤拷要锟斤拷(ji锟斤拷)锟絚

锟組锟斤拷"锟竭匡拷锟絎"微锟脚癸拷锟斤拷號