[Toán 11]

V

vitcon51193

lam them cach thông thương nha
tan x= sinx : cosx
tan2x = sin2x : cos2x
tan3x= sin3x : cos3x
bạn nhóm tanx + tan2x = công thức cộng
sẽ ra sin3x : cosxcos2x va = vế tan3x kia . rồi làm tiếp nha
 
C

connguoivietnam

tanx + tan2x - tan3x = 0 (đk cosx,cos2x,cos3x#0)
(sin3x/cosxcos2x)-(sin3x/cos3x)=0
sin3x((1/cosxcos2x)-(1/cos3x))=0
sin3x=0
cosxcos2x=cos3x
cosxcos2x=cos(2x+x)
cosxcos2x=cosxcos2x-sinxsin2x
sinxsin2x=0
 
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