Ta có:\(\frac{a}{b}=\frac{c}{d}\Rightarrow\frac{ad}{bd}=\frac{bc}{bd}\Rightarrow ad=bc\Rightarrow\frac{a}{c}=\frac{b}{d}\)
ai mk mk lại
bài 1: cho tỉ lệ thức \(\frac{a}{b}=\frac{c}{d}\)
a) CMR: (a+2c)(b+d)=(a+c)(b+2d) \(\left(b,d\ne0\right)\)
b) CMR: (a+c)(b-d)=ab-cd
c) CMR: \(\frac{a}{a-b}=\frac{c}{c-d}\left(a,b,c,d>0;a\ne b,c\ne d\right)\)
bài 2: cho \(\frac{a}{b}=\frac{b}{c}=\frac{c}{d}CMR:\left(\frac{a+b+c}{b+c+d}\right)^3=\frac{a}{d}\)
\(cho\frac{a}{b}=\frac{c}{d}\left(b:d>0\right).CMR\frac{a}{b}=\frac{a+c}{b+d}và\frac{c}{d}=\frac{c-a}{c-d}\)
Cho a,b,c,d thỏa mãn $\frac{a}{b}$ =$\frac{b}{c}$ =$\frac{c}{d}$ =$\frac{d}{a}$
CMR:($\frac{2019b+2020c-2021d}{2019c+2020d-2021e}$)^3=$\frac{a^2}{bc}$
Bài 1:Cho a;b;c;d thỏa mãn
(a+b+c+d)(a-b-c+d)=(a-b+c-d)(a+d-c-d)
CMR:a;b;c;d lập được thành tỉ lệ thức
Bài 2:Cho\(\frac{x}{a+2b+c}=\frac{y}{2a+b-c}=\frac{z}{4a-4b+c}\)
CMR:\(\frac{a}{x+2y+z}=\frac{b}{2x+y-c}=\frac{c}{4x-4y+z}\)
Bài 3:Cho\(\frac{1}{c}=\frac{1}{2}\left(\frac{1}{a}+\frac{1}{b}\right)CMR:\frac{a}{b}=\frac{a-c}{c-b}\)
\(Cho\frac{a}{b}
\(Cho\frac{a}{b}
Cho: \(\frac{a}{b}=\frac{b}{c}=\frac{c}{a}.CMR:\left(\frac{a+b+c}{b+c+d}\right)^3=\frac{a}{d}\)
\(Cho\frac{a}{b}=\frac{b}{c}=\frac{c}{d}.cmr\left(\frac{a+b+c}{b+c+d}\right)^3=\frac{a}{d}\)
\(cho\frac{a}{b}=\frac{b}{c}=\frac{c}{d}.CMR:\left(\frac{a+b+c}{b+c+d}\right)^3=\frac{a}{d}\)
Cho a,b,c,d>0.CMR:\(M=\frac{a}{b+c+d}+\frac{b}{a+c+d}+\frac{c}{a+b+d}+\frac{d}{a+b+c}\)Không là số tự nhiên