A
anhtraj_no1
Chứng minh Trong mọi tam giác ABC
1.
tanA+tanB+tanC=tanAtanBtanC
2.
cotAcotB+cotBcotC+cotCcotA=1
3.
sinBsinCcosA+sinCsinAcosB+sinAsinBcosC=2
4.
cos2Bcos2Csin2A+cos2Ccos2Asin2B+cos2Acos2Bsin2C=2
1.
tanA+tanB+tanC=tanAtanBtanC
2.
cotAcotB+cotBcotC+cotCcotA=1
3.
sinBsinCcosA+sinCsinAcosB+sinAsinBcosC=2
4.
cos2Bcos2Csin2A+cos2Ccos2Asin2B+cos2Acos2Bsin2C=2