1 phần 2 của 1 phần 6 cuan516
Hãy nhập câu hỏi của bạn vào đây, nếu là tài khoản VIP, bạn sẽ được ưu tiên trả lời.
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
Bạn nên gõ đề bằng công thức toán (biểu tượng $\sum$ góc trái khung soạn thảo) để mọi người hiểu đề của bạn hơn nhé.
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
Bạn nên viết đề bằng công thức toán (biểu tượng $\sum$ góc trái khung soạn thảo để được hỗ trợ tốt hơn. Viết ntn nhìn rất khó đọc
1: =>x-3+3x-9-2(3-x)=60
=>4x-12-6+2x=60
=>6x-18=60
=>6x=78
=>x=13
2: ĐKXĐ: x<>-1; x<>3
![](https://rs.olm.vn/images/avt/0.png?1311)
a, \(\dfrac{-3}{5}+\dfrac{5}{7}\)
\(=\dfrac{4}{35}\)
b, \(-5+\dfrac{1}{6}\)
= \(\dfrac{-29}{6}\)
c, \(\dfrac{1}{8}-\dfrac{1}{2}\)
= \(\dfrac{-3}{8}\)
c, \(\dfrac{5}{12}-\dfrac{-7}{6}\)
= \(\dfrac{19}{12}\)
d, \(-2.\dfrac{3}{7}\)
= \(\dfrac{-6}{7}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(a,MSC:3\)
Vì \(2>1\)
\(\Rightarrow\dfrac{2}{3}>\dfrac{1}{3}\)
\(b,MSC:42\\ \dfrac{4}{6}=\dfrac{4.7}{6.7}=\dfrac{28}{42}\\ \dfrac{4}{7}=\dfrac{4.6}{7.6}=\dfrac{24}{42}\)
Vì \(28>24\\ \Rightarrow\dfrac{4}{6}>\dfrac{4}{7}\)
\(c,MSC:22\)
\(\dfrac{6}{11}=\dfrac{6.2}{11.2}=\dfrac{12}{22}=\dfrac{12}{22}\\ \Rightarrow\dfrac{6}{11}=\dfrac{12}{22}\)
\(d,MSC:2\\ 1=\dfrac{2}{2}\)
Vì \(3>2\\ \Rightarrow\dfrac{3}{2}>1\)
![](https://rs.olm.vn/images/avt/0.png?1311)
Abcfsgsgsgsgsggggggghyhjgfhnhgjfgefhefrgjhfgjhergfyebfqybrfjyebrfyerbfjqyrfgjyerqfyearfyaberjybqrfjhwqdicuvdaciuvicvdcu
![](https://rs.olm.vn/images/avt/0.png?1311)
Bài 1 :Bỏ dấu ngoặc
2007-(7-3+4)
= 2007 -7+3-4
= 1999
6+[(-5) + 4 - 1 ]
= 6-5+4-1
=4
5-[(-6+8-2]
= 5+6-8+2
=5
-10+(7-3+1)
= -10 +7-3+1
= -5
Bài 3 Tìm x
\(\dfrac{1}{3} = \dfrac{x}{6}\)
\(<=> x= \dfrac{1.6}{3}\)
\(<=> x=2\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\dfrac{1}{2}+\dfrac{1}{6}+\dfrac{1}{12}+\dfrac{1}{20}+\dfrac{1}{30}+\dfrac{1}{42}+\dfrac{1}{56}=\dfrac{1}{2}+\dfrac{1}{2.3}+\dfrac{1}{3.4}+\dfrac{1}{4.5}+\dfrac{1}{5.6}+\dfrac{1}{6.7}+\dfrac{1}{7.8}\\ =\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{6}+\dfrac{1}{6}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{8}\\ =\left(-\dfrac{1}{3}+\dfrac{1}{3}\right)+\left(-\dfrac{1}{4}+\dfrac{1}{4}\right)+\left(-\dfrac{1}{5}+\dfrac{1}{5}\right)+\left(-\dfrac{1}{6}+\dfrac{1}{6}\right)+\left(-\dfrac{1}{7}+\dfrac{1}{7}\right)+\left(\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{8}\right)\\ =\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{8}=1-\dfrac{1}{8}=\dfrac{8-1}{8}=\dfrac{7}{8}\)
`@` `\text {Ans}`
`\downarrow`
\(\dfrac{1}{2}+\dfrac{1}{6}+\dfrac{1}{12}+\dfrac{1}{20}+\dfrac{1}{30}+\dfrac{1}{42}+\dfrac{1}{56}\)
`=`\(\dfrac{1}{1\times2}+\dfrac{1}{2\times3}+\dfrac{1}{3\times4}+\dfrac{1}{4\times5}+\dfrac{1}{5\times6}+\dfrac{1}{6\times7}+\dfrac{1}{7\times8}\)
`=`\(1-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+\dfrac{1}{4}+...+\dfrac{1}{7}-\dfrac{1}{8}\)
`=`\(1-\dfrac{1}{8}\)
`=`\(\dfrac{7}{8}\)