cm:a=b=c

P

parkjiyeon1999

Ta có: $a^2 + b^2 + c^2$-ab -bc -ac = 0

\Leftrightarrow $2a^2 + 2b^2 + 2c^2$- 2ab -2bc -2ac = 0

\Leftrightarrow $(a^2 -2ab + b^2)^2 + (b^2-2bc +c^2)^2 + (a^2 -2ac +c^2)^2$ = 0

\Leftrightarrow$(a-b)^2+(b-c)^2 +(a-c)^2$ = 0

\Leftrightarrow a-b = 0
a-c = 0
b-c = 0

\Leftrightarrow a=b=c (đpcm)
 
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