[Toán lớp 7] Tỉ lệ thức

E

emlakinhen@gmail.com

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D

deadguy

$\frac{a}{a+b+c+d}<\frac{a}{a+b+c}< \frac{a+d}{a+b+c+d}$

$\frac{b}{a+b+c+d}<\frac{b}{b+c+d}<\frac{a+b}{a+b+c+d}$

$\frac{c}{a+b+c+d}<\frac{c}{c+d+a}<\frac{c+b}{a+b+c+d}$

$\frac{d}{a+b+c+d}<\frac{d}{d+a+b}<\frac{d+c}{a+b+c+d}$
Từ đây suy ra dpcm
 
T

transformers123

cách khác:
$\dfrac{a}{a+b+c+d} < \dfrac{a}{a+b+c} < \dfrac{a}{a+c}$
$\dfrac{c}{a+b+c+d} < \dfrac{c}{c+d+a} < \dfrac{c}{a+c}$
$\dfrac{b}{a+b+c+d} < \dfrac{b}{b+c+d} < \dfrac{b}{b+d}$
$\dfrac{d}{c+d+a+b} < \dfrac{d}{d+a+b} < \dfrac{d}{b+d}$
cộng lại, ta có: $\mathfrak{dpcm}$
 
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