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\(A=\frac{1}{1.2}+\frac{1}{3.4}+\frac{1}{5.6}+..........+\frac{1}{49.50}\)
\(\Leftrightarrow A=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+..........+\frac{1}{49}-\frac{1}{50}\)
\(\Leftrightarrow A=1-\frac{1}{50}=\frac{49}{50}\)
cái kia tự tìm
![](https://rs.olm.vn/images/avt/0.png?1311)
các bạn ơi mình đang cần gấp . Mình chỉ còn 20 phút thui . HUHU
Bài làm :
1) \(\frac{x+11}{4}=\frac{2x+4}{5}\)
\(\Leftrightarrow\left(x+11\right).5=4.\left(2x+4\right)\)
\(\Leftrightarrow5x+55=8x+16\)
\(\Leftrightarrow5x-8x=16-55\)
\(\Leftrightarrow-3x=-39\)
\(\Leftrightarrow x=\frac{-39}{-3}=\frac{39}{3}=13\)
2)\(\frac{x+4}{x+10}=\frac{3}{5}\)
\(\Leftrightarrow\left(x+4\right).5=\left(x+10\right).3\)
\(\Leftrightarrow5x+20=3x+30\)
\(\Leftrightarrow5x-3x=30-20\)
\(\Leftrightarrow2x=10\)
\(\Leftrightarrow x=\frac{10}{2}=5\)
3)\(\frac{x+8}{x+14}=\frac{2}{3}\)
\(\Leftrightarrow\left(x+8\right).3=\left(x+14\right).2\)
\(\Leftrightarrow3x+24=2x+28\)
\(\Leftrightarrow3x-2x=28-24\)
\(\Leftrightarrow x=4\)
![](https://rs.olm.vn/images/avt/0.png?1311)
Ta có :
\(x.8=6.5\)
=> \(x=6.5:8\)
\(x=30:8=\frac{15}{4}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(|x-\frac{1}{3}|=\frac{5}{6}\)
\(\Rightarrow x-\frac{1}{3}=\frac{5}{6}\) hoặc \(x-\frac{1}{3}=-\frac{5}{6}\)
\(\Rightarrow x=\frac{5}{6}+\frac{1}{3}\) hoặc \(x=-\frac{5}{6}+\frac{1}{3}\)
\(\Rightarrow x=\frac{7}{6}\) hoặc \(x=-\frac{3}{6}=-\frac{1}{2}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
có \(\frac{4}{y}=\frac{3}{9}\)
\(=>y=\frac{4.9}{3}=12\)
\(\frac{x}{-6}=\frac{4}{12}\)
\(x=\frac{-6.4}{12}\)
=> x = -2
chúc bạn học tốt >_<