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\(\dfrac{3}{x-5}=\dfrac{-4}{x+2}\left(x\ne5;-2\right).\\ \Leftrightarrow\dfrac{3}{x-5}+\dfrac{4}{x+2}=0.\\ \Leftrightarrow\dfrac{3x+6+4x-20}{\left(x-5\right)\left(x+2\right)}=0.\\ \Rightarrow7x=14.\\ \Leftrightarrow x=2\left(TM\right).\)
![](https://rs.olm.vn/images/avt/0.png?1311)
a) Ta có: 2x+33=-11
nên 2x=-44
hay x=-22
b) Ta có: \(\dfrac{x}{2}=\dfrac{-49}{14}\)
nên x=-7
c) Ta có: \(\dfrac{5}{6}x+\dfrac{10}{3}=\dfrac{7}{2}\)
nên \(\dfrac{5}{6}x=\dfrac{7}{2}-\dfrac{10}{3}=\dfrac{1}{6}\)
hay \(x=\dfrac{1}{6}:\dfrac{5}{6}=\dfrac{1}{5}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(a,50\%x-0,2+x=\dfrac{4}{5}\)
\(\Leftrightarrow\dfrac{1}{2}x-0,2+x=\dfrac{4}{5}\)
\(\Leftrightarrow\dfrac{1}{2}x+x=\dfrac{4}{5}+0,2\)
\(\Leftrightarrow\dfrac{3}{2}x=\dfrac{4}{5}+\dfrac{1}{5}\)
\(\Leftrightarrow\dfrac{3}{2}x=1\)
\(\Leftrightarrow x=\dfrac{2}{3}\)
\(b,\left(x-\dfrac{3}{4}\right):\dfrac{1}{2}+\dfrac{3}{2}=\dfrac{25}{2}\)
\(\Leftrightarrow\left(x-\dfrac{3}{4}\right).2=\dfrac{25}{2}-\dfrac{3}{2}\)
\(\Leftrightarrow\left(x-\dfrac{3}{4}\right).2=\dfrac{22}{2}\)
\(\Leftrightarrow x-\dfrac{3}{4}=11:2\)
\(\Leftrightarrow x=\dfrac{11}{2}+\dfrac{3}{4}\)
\(\Leftrightarrow x=\dfrac{25}{4}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
B=(1/11+1/12+...+1/20)+(1/21+...+1/30)+(1/31+1/32+...+1/40)+...+(1/61+1/62+...+1/70)
=>B<1/10*10+1/20*10+...+1/60*10
=>B<1+1/2+...+1/6
=>B<1+1/2+1/3+1/6+1/4+1/5
=>B<5/2
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\dfrac{6^x}{3^3\cdot4}=2\)
=>6^x=2*4*3^3=8*3^3=6^3
=>x=3
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\dfrac{2x}{14}-\dfrac{x}{14}=-\dfrac{21}{14}\)
\(2x-x=-21\)
\(x=-21\)
![](https://rs.olm.vn/images/avt/0.png?1311)
(1 + 2 + 3 + ... + 31 + 32) : 11 + 2
= [(32 + 1).(32 - 1 + 1) : 2] : 11 + 2
= (33 . 32 : 2) : 11 + 2
= 33 . 16 : 11 + 2
= 3 . 16 + 2
= 48 + 2
= 50
x - 5 = ( -11) + (-4)
x - 5 = (-15)
x = (-15) + 5
x = (-10)
lxl = 2
=> x = -2 ; x = 2
x - 5 = (-11) + (-4)
=> x - 5 = (-15)
=> x = (-15) + 5
=> x = -10
Vậy x = -10