rút gọn vân dụng phân thức

A

angleofdarkness

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

Tương tự $b^2+(b-c)^2=2.(b-c).(a+b-c).$

\Rightarrow $M=\dfrac{a^2+(a-c)^2}{b^2+(b-c)^2}=\dfrac{a-c}{b-c}.$
 
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