Question

Tìm x

a) 7/x=x/28

b) 10+x/17+x=3/4

c)40+x/77-x=6/7

Answer 1

Lời giải:

a. $\frac{7}{x}=\frac{x}{28}$
$\Rightarrow x^2=7.28=196=14^2=(-14)^2$

$\Rightarrow x=\pm 14$

b. 

$\frac{x+10}{x+17}=\frac{3}{4}$

$\Rightarrow 4(x+10)=3(x+17)$

$\Rightarrow 4x+40=3x+51$

$\Rightarrow x=11$

c.

$\frac{40+x}{77-x}=\frac{6}{7}$

$\Rightarrow 7(40+x)=6(77-x)$
$\Rightarrow 280+7x=462-6x$

$\Rightarrow 13x=182$

$\Rightarrow x=182:13=14$

Answer 2

Lời giải:

a. $\frac{7}{x}=\frac{x}{28}$
$\Rightarrow x^2=7.28=196=14^2=(-14)^2$

$\Rightarrow x=\pm 14$

b. 

$\frac{x+10}{x+17}=\frac{3}{4}$

$\Rightarrow 4(x+10)=3(x+17)$

$\Rightarrow 4x+40=3x+51$

$\Rightarrow x=11$

c.

$\frac{40+x}{77-x}=\frac{6}{7}$

$\Rightarrow 7(40+x)=6(77-x)$
$\Rightarrow 280+7x=462-6x$

$\Rightarrow 13x=182$

$\Rightarrow x=182:13=14$