tìm x:
x = 2/3/7 x 1/2 -1/2x3/7+1/3
ai nhanh mk bấm likeeeeeeeeeeeeeeeeeeeeeee
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29 tháng 10 2021
1) \(x:\dfrac{1}{3}=\dfrac{1}{2}+\dfrac{1}{3}\)
\(\Rightarrow3\times x=\dfrac{5}{6}\Rightarrow x=\dfrac{5}{18}\)
2) \(\left(x:\dfrac{2}{3}\right):\dfrac{2}{5}=\dfrac{7}{10}\)
\(\Rightarrow\dfrac{3}{2}\times x=\dfrac{7}{10}\times\dfrac{2}{5}=\dfrac{7}{25}\)
\(\Rightarrow x=\dfrac{7}{25}:\dfrac{3}{2}=\dfrac{14}{75}\)
DT
19 tháng 3 2022
\(x-\dfrac{1}{4}=\dfrac{-21}{10}\)
\(x=\dfrac{-21}{10}+\dfrac{1}{4}\)
\(x=\dfrac{-42}{20}+\dfrac{5}{20}=\dfrac{-37}{20}\)
TT
2
21 tháng 10 2021
Bài 2:
Ta có: \(x\left(x-4\right)-x^2+8=0\)
\(\Leftrightarrow x^2-4x-x^2+8=0\)
\(\Leftrightarrow-4x=-8\)
hay x=2
HV
1
29 tháng 9 2016
\(6x\left(1-3x\right)+9x\left(2x-7\right)+171=0\)
\(\Leftrightarrow6x-18x^2+18x^2-63x+171=0\)
\(\Leftrightarrow-57x=-171\)
\(\Leftrightarrow x=3\)
\(\frac{x+1}{2015}+\frac{x+2}{2014}=\frac{x+3}{2013}+\frac{x+4}{2012}\)
\(\Leftrightarrow\left(\frac{x+1}{2015}+1\right)+\left(\frac{x+2}{2014}+1\right)-\left(\frac{x+3}{2013}+1\right)-\left(\frac{x+4}{2012}+1\right)=0\)
\(\Leftrightarrow\)\(\frac{x+2016}{2015}+\frac{x+2016}{2014}-\frac{x+2016}{2013}+\frac{x+2016}{2012}=0\)
\(\Leftrightarrow\left(x+2016\right)\left(\frac{1}{2015}+\frac{1}{2014}-\frac{1}{2013}-\frac{1}{2012}\right)=0\)
\(\Leftrightarrow x+2016=0\) ( vì \(\frac{1}{2015}+\frac{1}{2014}-\frac{1}{2013}-\frac{1}{2012}\ne0\) )
\(\Leftrightarrow x=-2016\)
15 tháng 10 2017
1. \(A=\left(2^{2017}\cdot3+2^{2017}\cdot5\right):2^{2018}\)
\(A=\left[2^{2017}.\left(3+5\right)\right]:\left(2^{2018}\right)\)
\(A=\left[2^{2017}.2^3\right]:\left(2^{2018}\right)\)
\(A=2^{2020}:2^{2018}=2^2=4\)
2. a) 2 + x : 5 = 6
=> x : 5 = 4
=> x = 20
b) 5x(7 + 48:x) = 45
=> x(7 + 48:x) = 9
=> 7x + 48 = 9
=> 7x = -39
=> x = -39/7.
c) Không hiểu đề câu này cho lắm.
3. \(25^{30}=\left(5^2\right)^{30}=5^{60};125^{19}=\left(5^3\right)^{19}=5^{57}\)
Vì 60 > 57 => \(25^{30}>125^{19}\)
4. \(S=1+7^1+...+7^{100}\)
\(\Rightarrow7S=7+7^2+...+7^{101}\)
\(\Rightarrow7S-S=7+7^2+...+7^{101}-1-7-...-7^{100}\)
\(\Rightarrow6S=7^{101}-1\)
\(\Rightarrow S=\frac{7^{101}-1}{6}\)
5. \(Q=1+2+2^2+...+2^{49}\)
\(\Rightarrow2Q=2+2^2+...+2^{50}\)
\(\Rightarrow2Q-Q=2+2^2+...+2^{50}-1-2-...-2^{49}\)
\(\Rightarrow Q=2^{50}-1\)
\(\Rightarrow2^{50}-1+1=2^n\)
\(\Rightarrow2^{50}=2^n\Rightarrow n=50\)
12 tháng 7 2017
Tìm x :
2,8 : x - 1,5 = 2,3 : 5,75
=> x - 1,5 = 5,75
x = 5,75 + 1,5
x = 7,25
Tính nhanh :
\(\frac{1}{1\times2}+\frac{1}{2\times3}+\frac{1}{3\times4}+...+\frac{1}{13\times14}\)
\(=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{13}-\frac{1}{14}\)
\(=1-\frac{1}{14}+0+...+0\)
\(=\frac{13}{14}\)
12 tháng 7 2017
1. 2,8 : x - 1,5 = 2,3 : 5,75
2,8 : x - 1,5 = 0,4
2,8 : x = 0,4 + 1,5
2,8 : x = 1,9
x = 2,8 : 1,9
x = 1,473
2. \(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{13.14}\)
= \(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{13}-\frac{1}{14}\)
= \(1-\frac{1}{14}\)
= \(\frac{13}{14}\)
X = \(2\frac{3}{7}\)X \(\frac{1}{2}\)- \(\frac{1}{2}\)X \(\frac{3}{7}\)+ \(\frac{1}{3}\)= \(\frac{17}{7}\)X \(\frac{1}{2}\)- \(\frac{1}{2}\)X \(\frac{3}{7}\)+ \(\frac{1}{3}\)
= \(\frac{17}{14}\)- \(\frac{3}{14}\)+ \(\frac{1}{3}\)
= 1 + \(\frac{1}{3}\)
= \(\frac{4}{3}\)
nhớ tk cho mk nha, mk trả lời sớm nhất