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1: =>0,5:(0,4-x)=2,5
=>0,4-x=0,5/2,5=0,5
=>x=0,4-0,5=-0,1
2: =>x*(3,6+6,4)=18,9
=>10x=18,9
=>x=1,89
3: =>(9,4+5,3):x=14
=>14,7:x=14
=>x=14,7/14=1,05
Lời giải:
$1,2+2,3+3,4+...+98,99+99,100=2,4x-1$
$(1+0,2)+(2+0,3)+(3+0,4)+...+(98+0,99)+(99+0,100)=2,4x-1$
$(1+2+3+...+98+99)+(0,2+0,3+0,4+...+0,99+0,100)=2,4x-1$
$=99.100:2 + (0,2+0,3+...+0,9)+(0,10+0,11+0,12+...+0,99)+0,1=2,4x-1$
$4950+0,1(2+3+...+9)+0,01(10+11+...+99)+0,1=2,4x-1$
$4950+0,1.44+0,01.4905+0,1=2,4x-1$
$5003,55=2,4x-1$
$x=\frac{100091}{48}$
Ta có: \(\left(\dfrac{1}{1\cdot2}+\dfrac{1}{2\cdot3}+\dfrac{1}{3\cdot4}+...+\dfrac{1}{8\cdot9}+\dfrac{1}{9\cdot10}\right)\cdot100-\left[\dfrac{5}{2}:\left(x+\dfrac{206}{100}\right)\right]:\dfrac{1}{2}=89\)
\(\Leftrightarrow100\cdot\dfrac{9}{10}-\left[\dfrac{5}{2}:\left(x+\dfrac{206}{100}\right)\right]:\dfrac{1}{2}=89\)
\(\Leftrightarrow\left[\dfrac{5}{2}:\left(x+\dfrac{103}{50}\right)\right]:\dfrac{1}{2}=1\)
\(\Leftrightarrow\dfrac{5}{2}:\left(x+\dfrac{103}{50}\right)=2\)
\(\Leftrightarrow x=-\dfrac{81}{100}\)
Bài 2:
a,\(|x-2|-3=-7\)
\(\Rightarrow|x-2|=-4\)
\(\Rightarrow x\in\varnothing\)
b,\(|x-5|+3=8\)
\(\Rightarrow|x-5|=5\)
\(\Rightarrow\left[{}\begin{matrix}x-5=5\\x-5=-5\end{matrix}\right.\)
\(\Rightarrow\left[{}\begin{matrix}x=10\\x=0\end{matrix}\right.\)
c,\(|x+3|-2+2x=5\)
\(\Rightarrow|x+3|+2x=7\)
\(\Rightarrow\left[{}\begin{matrix}x+3=2x=7,x+3\ge0\\-\left(x+3\right)+2x=7,x+3< 0\end{matrix}\right.\)
\(\Rightarrow\left[{}\begin{matrix}x=\frac{4}{3}\\x=10,x< -3\end{matrix}\right.,x\ge-3\)
\(\Rightarrow\left[{}\begin{matrix}x=\frac{4}{3}\\x\in\varnothing\end{matrix}\right.\)
d,\(|x-3,1|+|y-1,2|=0\)
Thay y =0
\(\Rightarrow|x-3,1|+|0-1,2|=0\)
\(\Rightarrow|x-3,1|+|-1,2|=0\)
\(\Rightarrow|x-3,1|+1,2=0\)
\(\Rightarrow|x-3,1|=-1,2\)
\(\Rightarrow x\in\varnothing\)
Bài 3:
a,(-2,7)+9-3,5)-1,2(-2)
=>-2,7-3,5+2,4
=>-3,8
b, (-2,3)(-0,4)-(-3,1)(-2,1)-13,2
=>0,92+3,1(-2,1)-13,2
=>0,92-6,51-13,2
=-18,79
\(x\cdot2,3+\dfrac{x}{10}=7,56\)
\(23x+x=75,6\)
\(x=3,15\)
a: =>2,4*x=7,56
=>x=2,4
b: =>x*4+x*11=1,8
=>15x=1,8
=>x=0,12
c: =>x*2,5-x*2=1,2
=>0,5*x=1,2
=>x=2,4
d: =>x*3,05-x*0,01=7,6
=>x*3,04=7,6
=>x=2,5
2x+30%x-2(x-1)=-1,2
2x+30%x-2x+2=-1,2
30%x+2=-1,2
30%x=-1,2-2
30%x=-3,2
(3/10)x=-3,2
X=-3,2÷(3/10)
X=(-32/10).(10/3)
X=-32/3
Vậy...
a,x.(76,42+23,58)=300
x.100=300
x=3
b,1,2.x=2,9-2,3
1,2.x=0,6
x=0,6:1,2
x=0,5
c,x:3,6=0,17:0,9
x:3,6=0,188888888
x=0,188888888.3,6
x=0,68
d, 1,2.x=5,34-0,54
1,2.x=4,8
x=4,8:1,2
x=4
đúng cho li ke nhé
a, X(76,42+23,58)=300
X.100=300
suy ra X =3
b,1,2.X=2,9-2,3
1,2.X=0,6
X=0,6:1,2
suy ra X=0,5
c,
X=0,17:0,9.3,6
suy ra X=0,68
d,1,2.X=5,34-0,54
1,2.X=4,8
X=4,8:1,2
X=4