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Tam giác ABC,
c/m:
$\sin A = \sin (B + C)$
$\cos \dfrac{A}{2} = \sin \dfrac{B + C}{2}$
$\tan A = - \tan(B + C)$
giúp m nhé
mai m thi r
c/m:
$\sin A = \sin (B + C)$
$\cos \dfrac{A}{2} = \sin \dfrac{B + C}{2}$
$\tan A = - \tan(B + C)$
giúp m nhé
mai m thi r
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