7.5:(x-2.5)+2.5=3
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a) 0.1+0.5+0.9+1.3+...+9.7+10.1
=(10.1+0.1)+...+(4.9+5.3)
=10.2+...+10.2
=10.2x13
=132.6
b) 2.5x4+20-5x2.5+7.5
=2.5x4+2.5x8-5x2.5+2.5x3
=2.5(4+8-5+3)
=2.5x10
=25
a) dãy số trên có 26 số hạng
tổng mỗi cặp số đầu và số cuối là 10.1+0.1 = 10.2
vậy tổng dãy trên là 10.2 x 26 : 2 = 81,6
b) 2.5 x 4 + 20 - 5 x 2,5 + 7,5
10 + 20 - 12,5 + 7,5
30 - 5
25
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\left|2x\right|-\left|-2,5\right|=\left|-7,5\right|\)
\(\left|2x\right|-2,5=7,5\)
|2x| = 7,5 + 2,5
|2x | = 10
TH1: 2x = 10
x=5
TH2: 2x= -10
x = -5
KL: x = 5 hoặc x = -5
\(\left|2x\right|-\left|-2\cdot5\right|=\left|-7\cdot5\right|\)
\(\Rightarrow\left|2x\right|-\left|-10\right|=\left|-35\right|\)
\(\Rightarrow\left|2x\right|-10=35\)
\(\Rightarrow\left|2x\right|=45\)
\(\Rightarrow\orbr{\begin{cases}2x=45\\2x=-45\end{cases}}\)
\(\Rightarrow\orbr{\begin{cases}x=22,5\\x=-22,5\end{cases}}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\left|2,5-x\right|=7,5\)
\(\orbr{\begin{cases}2,5-x=7,5\\2,5-x=-7,5\end{cases}}\)
\(\Rightarrow\orbr{\begin{cases}x=2,5-7,5\\x=2,5+7,5\end{cases}}\)
\(\Rightarrow\orbr{\begin{cases}x=-5\\x=10\end{cases}}\)
\(Vayx\in\left\{-5;10\right\}\)
\(1,6-\left|x-0,2\right|=0\)
\(\left|x-0,2\right|=1,6\)
\(\orbr{\begin{cases}x-0,2=1,6\\x-0,2=-1,6\end{cases}}\)
\(\Rightarrow\orbr{\begin{cases}x=1,6+0,2\\x=-1,6+0,2\end{cases}}\)
\(\Rightarrow\orbr{\begin{cases}x=1,8\\x=-1,4\end{cases}}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(A=\dfrac{6^{12}.3^3.5-7.9^7.2^{13}}{2.4^7.5-2^{14}.3^2}\)
\(=\dfrac{2^{12}.3^{12}.3^3.5-7.3^{14}.2^{12}}{2.2^{14}.5-2^{14}.3^2}\)
\(=\dfrac{2^{12}.3^{15}.5-7.3^{14}.2^{13}}{2.3^{14}.5-2^{14}.3^2}\)
\(=\dfrac{2^{12}.3^{14}.\left(15-14\right)}{2^{14}.\left(2.5-3\right)}\)
\(=\dfrac{3^{14}.1}{2^2}\)
\(=\dfrac{314}{4}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
Giải:
a) \(\left(\dfrac{1}{x}-3\right)\left(\dfrac{2}{3}x+\dfrac{1}{2}\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}\dfrac{1}{2}x-3=0\\\dfrac{2}{3}x+\dfrac{1}{2}=0\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}\dfrac{1}{2}x=3\\\dfrac{2}{3}x=-\dfrac{1}{2}\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}x=3\\x=-\dfrac{3}{4}\end{matrix}\right.\)
Vậy ...
b) \(\left|2x\right|-\left|-2,5\right|=\left|-7,5\right|\)
\(\Leftrightarrow\left|2x\right|-2,5=7,5\)
\(\Leftrightarrow\left|2x\right|=10\)
\(\Leftrightarrow\left[{}\begin{matrix}2x=10\\2x=-10\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}x=5\\x=-5\end{matrix}\right.\)
Vây ...
c) \(x-7\ge0\Leftrightarrow x\ge7\)
\(\left|1-3x\right|=x-7\)
\(\Leftrightarrow\left[{}\begin{matrix}1-3x=x-7\\1-3x=7-x\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}-3x-x=-7-1\\-3x+x=7-1\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}-4x=-8\\-2x=6\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}x=2\left(l\right)\\x=-3\left(l\right)\end{matrix}\right.\)
Vậy ...
![](https://rs.olm.vn/images/avt/0.png?1311)
{ x2 - [ 62 - ( 82 - 9.7)3 - 7.5]3 - 5.3 }3 = 1
{ x2 + [ 36 - (64 - 63)3 - 35]3 - 15}3 = 1
[ x2 - ( 36 - 13 - 35 ) - 15 ]3 = 1
[ x2 - ( 36 - 1 - 35 ) - 15]3 = 1
[ x2 - ( 35 - 35 ) - 15]3 = 1
[ x2 - 0 - 15]3 = 1
( x2 - 15 )3 = 1
<=> ( x2 - 15)3 = 13
=> x2 - 15 = 1
<=> x2 = 16
=> x = 4
7.5:(x-2.5)+2.5=3
35:(x-10)+10=3
35:(x-10)=3-10
35:(x-10)=-7
x-10=35:(-7)
x-10 = 5
x= 5+10
x=15
Vậy x = 15
Tick mình nhé nguyen duc duong![](/images/avt/avt5/avt490745_60by60.jpg)
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