Hãy nhập câu hỏi của bạn vào đây, nếu là tài khoản VIP, bạn sẽ được ưu tiên trả lời.
Biết a=b=c=d
Thay vào M
Ta có:
\(M=\frac{2a-a}{a+a}+\frac{2a-a}{a+a}+\frac{2a-a}{a+a}+\frac{2a-a}{a+a}\)
\(=4.\frac{2a-a}{a+a}=4.\frac{a}{2a}=4.\frac{1}{2}=2\)
\(\dfrac{a}{b}=\dfrac{c}{d}\Leftrightarrow ad=bc\)
Ta có:
Nếu:
\(\dfrac{2a+c}{2b+d}=\dfrac{a-c}{b-d}\Leftrightarrow\left(2a+c\right)\left(b-d\right)=\left(a-c\right)\left(2b+d\right)\)
\(\Leftrightarrow2a\left(b-d\right)+c\left(b-d\right)=a\left(2b+d\right)-c\left(2b+d\right)\)
\(\Leftrightarrow2ab-2ad+bc-cd=2ab+ad-2bc+cd\)
\(\Leftrightarrow ad=bc\)
\(\Leftrightarrow\dfrac{2a+c}{2b+d}=\dfrac{a-c}{b-d}\left(đpcm\right)\)
\(\dfrac{a}{2}=\dfrac{b}{3}\Rightarrow b=\dfrac{3}{2}a\)
\(\dfrac{a}{2}=\dfrac{c}{5}\Rightarrow c=\dfrac{5}{2}a\)
=>B=\(\dfrac{a+7\cdot\left(\dfrac{3}{2}a\right)-2\cdot\left(\dfrac{5}{2}a\right)}{3a+2\cdot\left(\dfrac{3}{2}a\right)-\dfrac{5}{2}a}=\dfrac{a+\dfrac{21}{2}a-5a}{3a+3a-\dfrac{5}{2}a}=\dfrac{\dfrac{13}{2}a}{\dfrac{7}{2}a}=\dfrac{13}{7}\)