[Toán lớp 7] Tỉ lệ thức

E

emlakinhen@gmail.com

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D

deadguy

aa+b+c+d<aa+b+c<a+da+b+c+d\frac{a}{a+b+c+d}<\frac{a}{a+b+c}< \frac{a+d}{a+b+c+d}

ba+b+c+d<bb+c+d<a+ba+b+c+d\frac{b}{a+b+c+d}<\frac{b}{b+c+d}<\frac{a+b}{a+b+c+d}

ca+b+c+d<cc+d+a<c+ba+b+c+d\frac{c}{a+b+c+d}<\frac{c}{c+d+a}<\frac{c+b}{a+b+c+d}

da+b+c+d<dd+a+b<d+ca+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:
aa+b+c+d<aa+b+c<aa+c\dfrac{a}{a+b+c+d} < \dfrac{a}{a+b+c} < \dfrac{a}{a+c}
ca+b+c+d<cc+d+a<ca+c\dfrac{c}{a+b+c+d} < \dfrac{c}{c+d+a} < \dfrac{c}{a+c}
ba+b+c+d<bb+c+d<bb+d\dfrac{b}{a+b+c+d} < \dfrac{b}{b+c+d} < \dfrac{b}{b+d}
dc+d+a+b<dd+a+b<db+d\dfrac{d}{c+d+a+b} < \dfrac{d}{d+a+b} < \dfrac{d}{b+d}
cộng lại, ta có: dpcm\mathfrak{dpcm}
 
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