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sweeet


Cho tam giac ABC. C/m:
a) $tan A+tanB+tanC = tanA.tanB.tanC$
B) $cotAcotB + cotBcotC + cotCcotA = 1$
C) $sin2A+sin2B+sin2C = 4sinAsinBsinC$
a) $tan A+tanB+tanC = tanA.tanB.tanC$
B) $cotAcotB + cotBcotC + cotCcotA = 1$
C) $sin2A+sin2B+sin2C = 4sinAsinBsinC$
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