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6 tháng 4 2018
Tìm x biết:
\(\frac{x}{3}-\frac{3}{4}=\frac{1}{12}\)
\(\frac{x}{3}=\frac{1}{12}+\frac{3}{4}\)
\(\frac{x}{3}=\frac{5}{6}\)
\(x=\frac{5}{6}.3\)
\(x=\frac{5}{2}\)
Vậy \(x=\frac{5}{2}\)
\(\frac{29}{30}-\left(\frac{13}{23}+x\right)=\frac{7}{69}\)
\(\frac{13}{23}+x=\frac{29}{30}-\frac{7}{69}\)
\(\frac{13}{23}+x=\frac{199}{230}\)
\(x=\frac{199}{230}-\frac{13}{23}\)
\(x=\frac{3}{10}\)
Vậy \(x=\frac{3}{10}\)
Bài 2: tính
\(\frac{1}{30}+\frac{1}{42}+\frac{1}{56}+\frac{1}{72}+\frac{1}{90}+\frac{1}{110}\)
\(=\frac{1}{5.6}+\frac{1}{6.7}+\frac{1}{7.8}+\frac{1}{8.9}+\frac{1}{9.10}+\frac{1}{10.11}\)
\(=\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+\frac{1}{7}-\frac{1}{8}+\frac{1}{8}-\frac{1}{9}+\frac{1}{9}-\frac{1}{10}+\frac{1}{10}-\frac{1}{11}\)
\(=\frac{1}{5}-\frac{1}{11}\)
\(=\frac{6}{55}\)
\(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{49.50}\)
\(=\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{49}-\frac{1}{50}\)
\(=\frac{1}{1}-\frac{1}{50}\)
\(=\frac{49}{50}\)
6 tháng 4 2018
Bài 2:
1/30+1/42+1/56+1/72+1/90+1/110
=1/5.6+1/6.7+1/7.8+1/8.9+1/9.10+1/10.11
=1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9+1/9-1/10+1/10-1/11
=1/5-1/11=6/55
b)1/1.2+1/2.3+...+1/49.50
=1-1/2+1/2-1/3+...+1/49-1/50
=1-1/50
=49/50
VT
29 tháng 3 2019
a) \(\frac{29}{30}\)- (\(\frac{13}{23}\)+X)=\(\frac{7}{69}\)
\(\frac{13}{23}\)+X=\(\frac{29}{30}\)-\(\frac{7}{69}\)
\(\frac{13}{23}\)+X=\(\frac{199}{230}\)
X=\(\frac{199}{230}\)-\(\frac{13}{23}\)
X=\(\frac{3}{10}\)
b)1/2+1/6+1/12+...+1/x(x+1)=2011/2012
=>1/1.2+1/2.3+1/3.4+...+1/x(x+1)=2011/2012
=>1-1/2+1/2-1/3+1/3+1/4+...+1/x+1/x+1=2011/2012
=>1-1/x+1=2011/2012
=>1/x+1=1-2011-2012
=>1/x+1=2012/2012-2011/2012
1/x+1=1/2012
=>x+1=2012
=>x=2011
25 tháng 3 2017
Bài1
a) 25/42 - 20/63 =5/18
b) 9/50 - 13/75 - 1/6 = -4/25
c) 2/15 - 2/65 - 4/39 = 0
Bài2
a) x + 7/12 =17/18-1/9 b) 29/30 - (18/23 + x)=7/69
x + 7/12 = 5/6 18/23 + x =29/30 - 7/69
x =5/6 - 7/12 18/23 +x = 199/230
x = 1/4 x = 199/230 - 18/23
x= 19/230
O
3
8 tháng 4 2015
13/23+x=29/30-7/69được mấy rồi trừ cho 13/23 là ra x thôi
MD
14 tháng 3 2017
\(\frac{29}{30}-\left(\frac{13}{23}+x\right)=\frac{7}{69}\)
\(\Rightarrow\left(\frac{29}{30}-\frac{7}{69}\right)=\frac{13}{23}+x\)
\(\Rightarrow\frac{199}{230}=\frac{13}{23}+x\)
\(x=\frac{199}{230}-\frac{13}{23}\)
\(x=\frac{3}{10}\)
11 tháng 4 2019
\(1,-\frac{3}{29}+\frac{-7}{29}\le\frac{x}{29}\le-\frac{3}{29}-\frac{5}{29}\)
\(\Rightarrow-\frac{10}{29}\le\frac{x}{29}\le-\frac{8}{29}\Rightarrow-10\le x\le-8\)
\(\Rightarrow x=\left\{-8;-9;-10\right\}\)
\(S=\frac{1}{2}+\frac{1}{2^2}+\frac{1}{2^3}+\frac{1}{2^4}+...+\frac{1}{2^{99}}+\frac{1}{2^{100}}\)
\(\Rightarrow2S=1+\frac{1}{2}+\frac{1}{2^2}+\frac{1}{2^3}+...+\frac{1}{2^{99}}\)
\(S=\frac{1}{2}+\frac{1}{2^2}+\frac{1}{2^3}+\frac{1}{2^4}+...+\frac{1}{2^{99}}+\frac{1}{2^{100}}\)
\(\Rightarrow2S-S=S=1-\frac{1}{2^{100}}\)
2 tháng 2 2019
\(a)\frac{62}{7}\cdot x=\frac{29}{9}\div\frac{3}{56}\)
\(\Rightarrow\frac{62}{7}\cdot x=\frac{29}{9}\cdot\frac{56}{3}\)
\(\Rightarrow\frac{62}{7}\cdot x=\frac{1624}{27}\)
\(\Rightarrow x=\frac{1624}{27}\div\frac{62}{7}\)
\(\Rightarrow x=\frac{1624}{27}\cdot\frac{7}{62}\)
\(\Rightarrow x=\frac{11368}{1674}=\frac{5684}{837}\)
Rút gọn thử đi
30 tháng 3 2018
a) \(x+\frac{7}{12}=\frac{17}{18}-\frac{1}{9}\)
\(\Rightarrow x+\frac{7}{12}=\frac{5}{6}\)
\(\Rightarrow x=\frac{5}{6}-\frac{7}{12}\)
\(\Rightarrow x=\frac{1}{4}\)
b) \(\frac{29}{30}-\left(\frac{13}{23}+x\right)=\frac{7}{69}\)
\(\Rightarrow\frac{13}{23}+x=\frac{29}{30}-\frac{7}{69}\)
\(\Rightarrow\frac{13}{23}+x=\frac{199}{230}\)
\(\Rightarrow x=\frac{199}{230}-\frac{13}{23}\)
\(\Rightarrow x=\frac{3}{10}\)
30 tháng 3 2018
a)\(x+\frac{7}{12}=\frac{17}{18}-\frac{1}{9}\)
\(x+\frac{7}{12}=\frac{5}{6}\)
\(x=\frac{5}{6}-\frac{7}{12}\)
\(x=\frac{1}{4}\)
b)\(\frac{29}{30}-\left(\frac{13}{23}+x\right)=\frac{7}{69}\)
\(\left(\frac{13}{23}+x\right)=\frac{29}{30}-\frac{7}{69}\)
\(\left(\frac{13}{23}+x\right)=\frac{199}{230}\)\(x=\frac{199}{230}-\frac{13}{23}\)
\(x=\frac{3}{10}\)