Tìm X biết 720:(X x 2 + X x 3) = 2x3
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720 : ( X x5 )= 6
X x 5 = 720 : 6
X x 5 =120
X = 120 : 5
X = 24
chúc bạn học tốt
720:(x.2+x.3)=2.3
=> 720:[x.(2+3)]=6
=> x.5 =720:6
=> x.5 =120
=> x =120:5
=> x =24
Vậy x=24
720 :[x +2 . x +3] =2.3
720:(x+2.x+3)=6
x+2.x+3=120
x.(2+3)=120
x.5=120
x=24
\(3^{x+1}+3^{x+2}=2^2.3^4\)
\(3^{x+1}+3.3^{x+1}=4.81\)
\(4.3^{x+1}=4.81\)
\(3^{x+1}=81=3^4\)
\(x+1=4\Rightarrow x=3\)
3x+25=26x22+2x30
3x+25=26x4+2
3x+25=106
3x=106-25=81
3x=34
⇒ x=4
a: =>41-(2x-5)=720:40=18
=>2x-5=23
=>2x=28
=>x=14
b: =>100x+5050=5750
=>100x=700
=>x=7
a: =>41-(2x-5)=720:40=18
=>2x-5=23
=>2x=28
=>x=14
b: =>100x+5050=5750
=>100x=700
=>x=7
b) \(\frac{1}{1.3}+\frac{1}{3.5}+\frac{1}{5.7}+...+\frac{1}{2013.2015}\)
\(=\frac{1}{2}\left(\frac{2}{1.3}+\frac{2}{3.5}+\frac{2}{5.7}+...+\frac{2}{2013.2015}\right)\)
\(=\frac{1}{2}\left(\frac{3-1}{1.3}+\frac{5-3}{3.5}+\frac{7-5}{5.7}+...+\frac{2015-2013}{2013.2015}\right)\)
\(=\frac{1}{2}\left(1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+...+\frac{1}{2013}-\frac{1}{2015}\right)\)
\(=\frac{1}{2}\left(1-\frac{1}{2015}\right)=\frac{1007}{2015}\)
Phương trình tương đương với:
\(\frac{1007X}{2015}=\frac{4}{2015}\Leftrightarrow X=\frac{4}{1007}\)
c) \(\frac{x+1}{2015}+\frac{x+2}{2016}=\frac{x+3}{2017}+\frac{x+4}{2018}\)
\(\Leftrightarrow\frac{x+1}{2015}-1+\frac{x+2}{2016}-1=\frac{x+3}{2017}-1+\frac{x+4}{2018}-1\)
\(\Leftrightarrow\frac{x-2014}{2015}+\frac{x-2014}{2016}=\frac{x-2014}{2017}+\frac{x-2014}{2018}\)
\(\Leftrightarrow x-2014=0\)
\(\Leftrightarrow x=2014\)
\(720:\left[41-\left(2x-5\right)\right]=40\) \(3x+8x-30=25\)
\(41-\left(2x-5\right)=18\) \(3x+8x=55\)
\(2x-5=23\) \(11x=55\)
\(2x=28\) \(x=5\)
\(x=14\)
\(720:\left(x\times2+x\times3\right)=2\times3\)
\(720:\left(x\times5\right)=6\)
\(x\times5=720:6\)
\(x\times5=120\)
\(x=120:5\)
\(x=24\)