Toán 7 : Tỉ lệ thức

P

phamhuy20011801

$1,$
$2x=3y \rightarrow \dfrac{x}{3}=\dfrac{y}{2} \rightarrow \dfrac{x}{6}=\dfrac{y}{4}$ $(1)$
$3y=4z-2y \rightarrow 5y=4z \rightarrow \dfrac{y}{4}=\dfrac{z}{5}$ $(2)$
Từ $(1)$ và $(2)$
$\rightarrow \dfrac{x}{6}=\dfrac{y}{4}=\dfrac{z}{5}=\dfrac{x+y+z}{6+4+5}=\dfrac{45}{15}=3$
$\rightarrow x=3.6=18 ; y=3.4=12 ; z=3.5=15$
$2,$ Tương tự...
 
V

vanmanh2001

Bài 1)
[TEX]2x = 3y \Rightarrow[/TEX] $\frac{x}{3} = \frac{y}{2}$
[TEX]5y = 4z \Rightarrow[/TEX] $\frac{y}{4} = \frac{z}{5}$
[TEX]\Rightarrow[/TEX] $\frac{2x}{6} = \frac{2y}{4} = \frac{2z}{5} = \frac{2x + 2y + 2z}{15}$
$= \frac{90}{15} = 6$
[TEX]\Rightarrow[/TEX] $x = 18 , y = 12 , z = 15$
 
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N

nhtbangchu

Tìm x trong các tỉ lệ thức

1) $\dfrac{37-x}{x+13}=\dfrac{5}{3}$

2) $\dfrac{2x-1}{3x+2}=\dfrac{2x+1}{3x-2}$
 
T

truongtuan2001

1)
$\frac{37-x}{x+13} = \frac{5}{3}$
\Leftrightarrow $3(37-x) = 5(x+13)$
\Leftrightarrow $111-3x = 5x + 65$
\Leftrightarrow $-8x = -46$
\Leftrightarrow $x = 5,75$
2)
$\frac{2x-1}{3x+2}$ = $\frac{2x+1}{3x-2}$
\Leftrightarrow $(2x-1)(3x-2) = (2x+1)(3x+2)$
\Leftrightarrow $6x^2 -7x +2 = 6x^2 +7x +2$
\Leftrightarrow $-14x = 0$
\Leftrightarrow $x=0$
 
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