[Toán 7] Violympic vòng 4

H

huuthuyenrop2

$\dfrac{3x- 1}{5- x}= \dfrac{3- 6x}{2x+ 3}$
\Leftrightarrow $(3x-1)(2x+3)=(3-6x)(5-x)$
\Leftrightarrow $6x^2+7x-3 = 15-33x+6x^2$
\Leftrightarrow $6x^2+7x+33x-6x^2=15+3$
\Leftrightarrow $40x=18$
\Leftrightarrow $x= 0,45$
 
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H

huuthuyenrop2

$\dfrac{2x+ 3}{5x+ 2}= \dfrac{4x+ 5}{10x+ 2}$

\Leftrightarrow $ (2x+3)(10x+2)=(5x+2)(4x+5)$

\Leftrightarrow $ 20x^2+34x+6= 20x^2 +33x+10$

\Leftrightarrow $ 20x^2+34x-33x-20x^2 = 10-6$

\Leftrightarrow $x= 4$


 
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