| Xét $K=[\frac{A}{-a+b+c},\frac{B}{a-b+c},\frac{C}{a+b-c}]=[\frac{A}{-a+b+c},\frac{M}{2a}] $
suy ra K thuộc AM tương tự K thuộc BN,CM
$K=[\frac{A}{-a+b+c},\frac{B}{a-b+c},\frac{C}{a+b-c}]=[[\frac{A}{a+b+c},\frac{B}{a+b+c},\frac{C}{a+b+c}],[\frac{A}{-2a},\frac{B}{-2b},\frac{C}{-2c}]]
=[\frac{G}{3(a+b+c)},\frac{I}{-2(a+b+c)}] $
suy ra K thuộc IG suy ra đpcm
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