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1 tháng 8 2020
a) \(\frac{x}{5}=\frac{2}{5}\Rightarrow x=\frac{2\cdot5}{5}=2\)
b)\(\frac{3}{8}=\frac{6}{x}\Rightarrow x=\frac{6\cdot8}{3}=16\)
c)\(\frac{1}{9}=\frac{x}{27}\Rightarrow x=\frac{27}{9}=3\)
d) \(\frac{4}{x}=\frac{8}{6}\Rightarrow x=\frac{4\cdot6}{8}=3\)
e)
\(\frac{3}{x-5}=-\frac{4}{x+2}\\ \Rightarrow3\left(x+2\right)=-4\left(x-5\right)\\ \Leftrightarrow3x+6=-4x+20\\ \Leftrightarrow3x+6+4x-20=0\\ \Leftrightarrow7x-14=0\\ \Leftrightarrow x=2\)
\(g,\frac{x}{-2}=-\frac{8}{x}\Rightarrow x^2=16\Leftrightarrow\left[{}\begin{matrix}x=4\\x=-4\end{matrix}\right.\)
Vậy có 2 giá trị của x là 4 ; -4
1 tháng 8 2020
a) Ta có: \(\frac{x}{5}=\frac{2}{5}\)
\(\Leftrightarrow x=\frac{2\cdot5}{5}=2\)
Vậy: x=2
b) Ta có: \(\frac{3}{8}=\frac{6}{x}\)
\(\Leftrightarrow x=\frac{6\cdot8}{3}=\frac{48}{3}=16\)
Vậy: x=16
c) Ta có: \(\frac{1}{9}=\frac{x}{27}\)
\(\Leftrightarrow x=\frac{1\cdot27}{9}=\frac{27}{9}=3\)
Vậy: x=3
d) Ta có: \(\frac{4}{x}=\frac{8}{6}\)
\(\Leftrightarrow x=\frac{4\cdot6}{8}=\frac{24}{8}=3\)
Vậy: x=3
e) Ta có: \(\frac{3}{x-5}=\frac{-4}{x+2}\)
\(\Leftrightarrow3\cdot\left(x+2\right)=-4\cdot\left(x-5\right)\)
\(\Leftrightarrow3x+6=-4x+20\)
\(\Leftrightarrow3x+6+4x-20=0\)
\(\Leftrightarrow7x-14=0\)
\(\Leftrightarrow7x=14\)
hay x=2
Vậy: x=2
g) Sửa đề: \(\frac{x}{-2}=\frac{-8}{x}\)
Ta có: \(\frac{x}{-2}=\frac{-8}{x}\)
\(\Leftrightarrow x^2=\left(-8\right)\cdot\left(-2\right)=16\)
hay x∈{4;-4}
Vậy: x∈{4;-4}
1 tháng 8 2018
a) \(\left(19x+2\times5^2\right):14=\left(13-8\right)^2-4^2\)
\(\Rightarrow\left(19x+50\right):14=5^2-4^2=25-16=9\)
\(\Rightarrow19x+50=126\)
\(\Rightarrow19x=76\Rightarrow x=4\)
Vậy x = 4
b) \(2\times3^2=10\times3^{12}+8\times27^4\)
\(\Rightarrow2\times3^2=10\times\left(3^3\right)^4+8\times27^4\)
\(\Rightarrow2\times3^2=27^4\times\left(10+8\right)\)
\(\Rightarrow18=27^4\times18\)
\(\Rightarrow27^4\times18-18=0\Rightarrow18\times\left(27^4-1\right)=0\)
=> Không thấy biến x đâu cả
c) Ta thấy 33 = 27
\(\Rightarrow3^{2x-5}=3^3\Rightarrow2x-5=3\Rightarrow2x=8\Rightarrow x=4\)
Vậy x = 4
d) \(3^{x+1}-x=80\Rightarrow3^{x+1}=81\)
Ta thấy 34 = 81
\(\Rightarrow3^{x+1}=3^4\Rightarrow x+1=4\Rightarrow x=3\)
Vậy x = 3
31 tháng 1 2022
a: \(\Leftrightarrow x^3=\dfrac{539}{64}\)
hay \(x=\dfrac{7\sqrt{11}}{4}\)
c: \(\Leftrightarrow2^{2x-1}=2^9\cdot2^2=2^{11}\)
=>2x-1=11
hay x=6
d: \(\Leftrightarrow x^{17}-x=0\)
\(\Leftrightarrow x\left(x-1\right)\left(x+1\right)=0\)
hay \(x\in\left\{0;1;-1\right\}\)
6 tháng 2 2018
bài này áp dụng quy tắc nhân chéo nha :vv
a) \(\dfrac{x}{5}=\dfrac{2}{5}\Leftrightarrow5x=2.5=10\Leftrightarrow x=\dfrac{10}{5}=2\)
b) \(\dfrac{3}{8}=\dfrac{6}{x}\Leftrightarrow3x=6.8=48\Leftrightarrow x=\dfrac{48}{3}=16\)
c)\(\dfrac{1}{9}=\dfrac{x}{27}\Leftrightarrow9x=27\Leftrightarrow x=\dfrac{27}{9}=3\)
d)\(\dfrac{4}{x}=\dfrac{8}{6}\Leftrightarrow8x=4.6=24\Leftrightarrow x=\dfrac{24}{8}=3\)
e) \(\dfrac{3}{x-5}=\dfrac{-4}{x+2}\Leftrightarrow3\left(x+2\right)=-4\left(x-5\right)\\ \Leftrightarrow3x+4x=-6+20\\ \Leftrightarrow7x=14\Leftrightarrow x=\dfrac{14}{7}=2\)
g) \(\dfrac{x}{-2}=\dfrac{-8}{x}\Leftrightarrow x^2=\left(-2\right)\left(-8\right)=16\\ \Rightarrow x=\pm4\)
G
12 tháng 2 2018
Giải:
a) \(\dfrac{4+x}{x+2}=\dfrac{8}{6}\)
\(\Leftrightarrow\dfrac{4+x}{x+2}=\dfrac{4}{3}\)
\(\Leftrightarrow3\left(4+x\right)=4\left(x+2\right)\)
\(\Leftrightarrow12+3x=4x+8\)
\(\Leftrightarrow4x-3x=12-8\)
\(\Leftrightarrow x=4\)
Vậy ...
b) \(\dfrac{3}{x-5}=\dfrac{-4}{x+2}\)
\(\Leftrightarrow3\left(x+2\right)=-4\left(x-5\right)\)
\(\Leftrightarrow3x+6=-4x+20\)
\(\Leftrightarrow7x=14\)
\(\Leftrightarrow x=\dfrac{14}{7}=2\)
Vậy ...
c) \(\dfrac{x}{-2}=\dfrac{-8}{x}\)
\(\Leftrightarrow x^2=\left(-2\right)\left(-8\right)\)
\(\Leftrightarrow x^2=16\)
\(\Leftrightarrow\left\{{}\begin{matrix}x=4\\x=-4\end{matrix}\right.\)
Vậy ...
18 tháng 7 2016
c) pt <=> \(x-\frac{21}{5}=\frac{23}{7}< =>x=\frac{23}{7}+\frac{21}{5}=\frac{262}{35}\)
vậy x = \(\frac{262}{35}\)
d) \(x-\frac{3}{4}=\frac{51}{8}< =>x=\frac{51}{8}+\frac{3}{4}=\frac{57}{8}\)
vậy x = \(\frac{57}{8}\)
e) pt <=> \(\frac{7}{8}:x=\frac{7}{2}< =>\frac{7}{8}.\frac{1}{x}=\frac{7}{2}< =>\frac{7}{8x}=\frac{7}{2}< =>56x=14< =>x=\frac{14}{56}=\frac{1}{4}\)
vậy x = \(\frac{1}{4}\)
18 tháng 7 2016
a) pt <=> \(x+\frac{11}{4}=\frac{17}{3}< =>x=\frac{17}{3}-\frac{11}{4}=\frac{35}{12}\)
vậy x = \(\frac{35}{12}\)
b) pt <=> \(\frac{x.7}{2}=\frac{19}{4}< =>x=\frac{19.2}{4.7}=\frac{38}{28}=\frac{19}{14}\)
vậy x = \(\frac{19}{14}\)
PA
28 tháng 11 2016
\(8-12x+6x^2-x^3\)
\(=\left(2-x\right)^3\)
\(125x^3-75x^2+15x-1\)
\(=\left(5x-1\right)^3\)
\(x^2-xz-9y^2+3yz\)
\(=\left(x-3y\right)\left(x+3y\right)-z\left(x-3y\right)\)
\(=\left(x-3y\right)\left(x+3y-z\right)\)
\(x^3-x^2-5x+125\)
\(=\left(x+5\right)\left(x^2-5x+25\right)-x\left(x+5\right)\)
\(=\left(x+5\right)\left(x^2-5x+25-x\right)\)
\(=\left(x+5\right)\left(x^2-6x+25\right)\)
\(x^3+2x^2-6x-27\)
\(=x^3+5x^2+9x-3x^2-15x-27\)
\(=x\left(x^2+5x+9\right)-3\left(x^2+5x+9\right)\)
\(=\left(x-3\right)\left(x^2+5x+9\right)\)
\(12x^3+4x^2-27x-9\)
\(=4x^2\left(3x+1\right)-9\left(3x+1\right)\)
\(=\left(3x+1\right)\left(4x^2-9\right)\)
\(=\left(3x+1\right)\left(2x-3\right)\left(2x+3\right)\)
\(4x^4+4x^3-x^2-x\)
\(=4x^3\left(x+1\right)-x\left(x+1\right)\)
\(=x\left(x+1\right)\left(4x^2-1\right)\)
\(=x\left(x+1\right)\left(2x-1\right)\left(2x+1\right)\)
Chọn B, D