[Toán 8]Tính $M=\dfrac{a+2b}{2a-b}$

S

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$2a^2+2b^2=5ab \leftrightarrow 2a^2+2b^2-5ab=0$

$\leftrightarrow 2a^2-ab-4ab+2b^2=(a-2b)(2a-b)=0$

Vì $a \neq 2b$ nên $a=2b$

Thay vào M ta được:

$M=\dfrac{a+2b}{2a-b}=\dfrac{2b+2b}{4b-b}=\dfrac{4}{3}$
 
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