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QK
6 tháng 8 2016
1)
\(\frac{7.8^3-5.2^{10}}{\left(-16\right)^2}\)
= \(\frac{7.2^8.2-5.2^8.2^2}{16^2}\)
= \(\frac{2^8.\left(2.7-5.2^2\right)}{2^8}\)
= \(\frac{2^8.\left(-6\right)}{2^8}\)
= \(-6\)
12 tháng 5 2022
Bài 1:
\(S=4\left(\dfrac{1}{1\cdot7}+\dfrac{1}{7\cdot13}+...+\dfrac{1}{43\cdot49}\right)\)
\(=\dfrac{4}{6}\left(\dfrac{6}{1\cdot7}+\dfrac{6}{7\cdot13}+...+\dfrac{6}{43\cdot49}\right)\)
\(=\dfrac{2}{3}\left(1-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{13}+...+\dfrac{1}{43}-\dfrac{1}{49}\right)\)
\(=\dfrac{2}{3}\cdot\dfrac{48}{49}=\dfrac{96}{147}=\dfrac{32}{49}\)
Bài 3:
Theo đề, ta có:
\(\dfrac{a}{b}=\dfrac{a+10}{b+10}\)
=>ab+10a=ab+10b
=>10a=10b
=>a/b=1
15 tháng 2 2017
\(\frac{-28}{4}\le x< \frac{-21}{7}=-7\le x< -3=\left\{-7;-6;-5;-4\right\}\)
27 tháng 4 2019
\(x-40\%x=3,6\)
\(\Rightarrow100\%x-40\%x=3,6\)
\(\Rightarrow60\%x=3,6\)
\(\Rightarrow\frac{60}{100}x=3,6\)
\(\Rightarrow x=6\)
27 tháng 4 2019
\(3\frac{2}{7}x-\frac{1}{3}=-2\frac{3}{4}\)
\(\Rightarrow\frac{23}{7}x-\frac{1}{3}=-\frac{11}{4}\)
\(\Rightarrow\frac{23}{7}x=-\frac{33}{12}+\frac{4}{12}\)
\(\Rightarrow\frac{23}{7}x=\frac{29}{12}\)
\(\Rightarrow x=\frac{29}{12}:\frac{23}{7}=\frac{203}{276}\)
29 tháng 1 2019
\(\frac{3}{x-5}=-\frac{4}{x+2}\)
\(\Leftrightarrow3\left(x+2\right)=-4\left(x-5\right)\)
\(\Leftrightarrow3x+6=-4x+20\)
\(\Leftrightarrow7x=14\)
\(\Leftrightarrow x=2\)
\(\frac{x}{-2}=-\frac{8}{x}\)
\(\Leftrightarrow x^2=16\)
\(\Leftrightarrow x=\pm4\)
\(-\frac{2}{x}=\frac{y}{3}\)
\(\Leftrightarrow xy=-6\)
\(\Leftrightarrow x;y\inƯ\left(-6\right)=\left\{\pm1;\pm2;\pm3;\pm6\right\}\)
Xét bảng
| x | 1 | -1 | 2 | -2 | 3 | -3 | 6 | -1 |
| y | -6 | 6 | -3 | 3 | -2 | 2 | -1 | 6 |
Vậy.................
\(\frac{2x-9}{240}=\frac{39}{80}\)
\(\Leftrightarrow2x-9=\frac{240.39}{80}\)
\(\Leftrightarrow2x-9=117\)
\(\Leftrightarrow2x=126\)
\(\Leftrightarrow x=63\)
16 tháng 2 2017
a) \(\frac{-28}{4}\le x\le\frac{-21}{7}\)
\(\Rightarrow-7\le x\le-3\)
\(\Rightarrow x=\left\{-3;-4;-5;-6;-7\right\}\)
b) \(\frac{-5}{12}=\frac{7}{72}\)
\(\Rightarrow-5.72=y.12\)
\(\Rightarrow y=\frac{-5.72}{12}\)
\(\Rightarrow y=-30\)
c) \(\frac{x}{19}=4\)
\(\Rightarrow x\div19=4\)
\(\Rightarrow x=4.19\)
\(\Rightarrow x=76\)
d) \(\frac{z+3}{15}=\frac{-1}{3}\)
\(\Rightarrow\left(z+3\right).3=-1.15\)
\(\Rightarrow z+3=\frac{-1.15}{3}\)
\(\Rightarrow z+3=-5\)
\(\Rightarrow z=-5-3\)
\(\Rightarrow z=-8\)
22 tháng 6 2020
a, \(\frac{-3}{5}+\frac{7}{21}+\frac{-4}{5}+\frac{7}{5}\)
\(=\left(\frac{-3}{5}+\frac{-4}{5}+\frac{7}{5}\right)+\frac{7}{21}\)
\(=0+\frac{7}{21}\)
\(=\frac{7}{21}\)
\(=\frac{1}{3}\)
b, \(\frac{8}{9}+\frac{1}{9}.\frac{7}{9}+\frac{1}{9}.\frac{2}{9}\)
\(=\frac{8}{9}+\frac{1}{9}.\left(\frac{7}{9}+\frac{2}{9}\right)\)
\(=\frac{8}{9}+\frac{1}{9}.1\)
\(=\frac{8}{9}+\frac{1}{9}\)
\(=1\)
22 tháng 6 2020
a) \(\frac{-3}{5}\)+\(\frac{7}{21}\)+\(\frac{-4}{5}\)+\(\frac{7}{5}\)
=(\(\frac{-3}{5}\)+\(\frac{-4}{5}\)+\(\frac{7}{5}\)) +\(\frac{7}{21}\)
= 0+
16 tháng 2 2016
A, Theo đề ta có 108/12 = 9 ; 91/7 = 13
Vì \(9\le x\le13\) nên \(x\in\left\{9;10;11;12;13\right\}\)
Vậy \(A=\left\{9;10;11;12;13\right\}\)
B, Theo đề ta có -28/4 = -7 ; -21/7 = -3
Vì \(-7\le x\le-3\) nên \(x\in\left\{-7;-6;-5;-4;-3\right\}\)
Vậy E = {-7 ; -6 ; -5 ; -4 ; -3}
16 tháng 2 2016
a) \(y=\frac{108}{12}\le x\le\frac{91}{7}\Rightarrow9\le x\le13\)=> E = {x\(\in N ; 9\le x\le13\)} => E = {9;10;11;12;13}
KN
2 tháng 5 2019
\(a.\frac{2}{x}=\frac{x}{8}\)
\(\Rightarrow x^2=2.8\)
\(\Rightarrow x^2=16\)
\(\Rightarrow x^2=4^2\)
\(\Rightarrow x=4\)
KN
2 tháng 5 2019
\(b.\frac{-28}{4}\le x\le\frac{-21}{7}\)
\(\Rightarrow\frac{-196}{28}\le\frac{28x}{28}\le\frac{-84}{28}\)
\(\Rightarrow-196\le28x\le-84\)
Mà \(28x⋮28\)
\(\Rightarrow28x\in\left\{-84;-112;-140;-168;-196\right\}\)
\(\Rightarrow x\in\left\{-3;-4;-5;-6;-7\right\}\)
NC
27 tháng 8 2020
a) Ta có: \(-x+\frac{4}{7}=\frac{1}{3}\)
\(\Leftrightarrow-x=-\frac{5}{21}\)
\(\Rightarrow x=\frac{5}{21}\)
b) Ta có: \(x\div\left(-\frac{1}{3}\right)^2=-\frac{1}{3}\)
\(\Rightarrow x=\left(-\frac{1}{3}\right)^3=-\frac{1}{27}\)
c) \(\left(\frac{3}{5}\right)^5.x=\left(\frac{3}{5}\right)^7\)
\(\Rightarrow x=\left(\frac{3}{5}\right)^2=\frac{9}{25}\)
27 tháng 8 2020
\(a.-x+\frac{4}{7}=\frac{1}{3}\)
\(-x=\frac{1}{3}-\frac{4}{7} \)
\(-x=\frac{7}{21}-\frac{12}{21}\)
\(-x=\frac{-5}{21}\)
\(x=\frac{5}{21}\)
\(b.x:\left(\frac{-1}{3}\right)^2=\frac{-1}{3}\)
\(x=\frac{-1}{3}.\left(\frac{-1}{3}\right)^2\)
\(x=\frac{-1}{3}.\frac{-1}{3}.\frac{-1}{3}\)
\(x=\frac{-1}{27}\)
\(c.\left(\frac{3}{5}\right)^5.x=\left(\frac{3}{5}\right)^7\)
\(x=\left(\frac{3}{5}\right)^7:\left(\frac{3}{5}\right)^5\)
\(x=\left(\frac{3}{5}\right)^2\)
\(x=\frac{3}{5}.\frac{3}{5}\)
\(x=\frac{9}{25}\)