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a)\(72.19 - 36^2:18= 72.19- 36.36:18\)
\(=72.19 - 72=72.(19 - 1)\)
\(=72.18=1296\)
b)
\(\begin{array}{l}750{\rm{ }}:{\rm{ }}\left\{ {130{\rm{ }} - {\rm{ }}[{{\left( {5.{\rm{ }}14{\rm{ }} - {\rm{ }}65} \right)}^3} + {\rm{ }}3} \right\}\\ = 750{\rm{ }}:{\rm{ }}\left\{ {130{\rm{ }} - {\rm{ }}\left[ {{{\left( {{\rm{70 }} - {\rm{ }}65} \right)}^3} + {\rm{ }}3} \right]} \right\}\\ = 750{\rm{ }}:{\rm{ }}\left\{ {130{\rm{ }} - {\rm{ }}\left[ {{5^3} + {\rm{ }}3} \right]} \right\}\\ = 750{\rm{ }}:{\rm{ }}\left\{ {130{\rm{ }} - {\rm{ }}\left[ {125 + {\rm{ }}3} \right]} \right\}\\ = 750{\rm{ }}:{\rm{ }}\left\{ {130{\rm{ }} - {\rm{ 128}}} \right\}\\ = 750:2 = 375.\end{array}\)

750 : {130 – [(5 . 14 – 65)3 + 3]}
= 750 : {130 – [(70 – 65)3 + 3]}
= 750 : {130 – [(5)3 + 3]}
= 750 : (130 – 128)
= 750 : 2
= 375

\(\frac{3^2}{5.14}+\frac{3^2}{7.18}+\frac{3^2}{9.22}+\frac{3^2}{11.26}+\frac{3^2}{13.30}\)
\(=3^2.2.\left(\frac{1}{10.14}+\frac{1}{14.18}+\frac{1}{18.22}+\frac{1}{22.26}+\frac{1}{26.30}\right)\)
\(=9.2.\frac{1}{4}.\left(\frac{14-10}{14.10}+\frac{18-14}{14.18}+\frac{22-18}{18.22}+\frac{26-22}{22.26}+\frac{30-26}{26.30}\right)\)
\(=\frac{9}{2}\left(\frac{1}{10}-\frac{1}{14}+\frac{1}{14}-\frac{1}{18}+\frac{1}{18}-\frac{1}{22}+\frac{1}{22}-\frac{1}{26}+\frac{1}{26}-\frac{1}{30}\right)\)
=\(\frac{9}{2}.\left(\frac{1}{10}-\frac{1}{30}\right)=\frac{9}{2}.\frac{1}{15}=\frac{3}{10}\)
\(\frac{3^2}{5.14}+\frac{3^2}{7.18}+\frac{3^2}{9.22}+\frac{3^2}{13.30}\)
= \(2.\left(\frac{3^2.}{5.2.14}+\frac{3^2}{2.7.18}+\frac{3^2}{2.9.22}+\frac{3^2}{2.13.30}\right)\)
= \(2.\left(\frac{3^2}{10.14}+\frac{3^2}{14.18}+\frac{3^2}{18.22}+\frac{3^2}{26.30}\right)\)
= \(2.\frac{3^2}{4}\left(\frac{4}{10.14}+\frac{4}{14.18}+\frac{4}{18.22}+\frac{4}{26.30}\right)\)
= \(\frac{9}{2}\left(\frac{1}{10}-\frac{1}{14}+\frac{1}{14}-\frac{1}{18}+\frac{1}{18}-\frac{1}{22}+\frac{1}{195}\right)\)
= \(\frac{9}{2}.\left(\frac{1}{10}-\frac{1}{22}+\frac{1}{195}\right)\)
= \(\frac{9}{2}.\left(\frac{3}{55}+\frac{1}{195}\right)\)
=\(\frac{9}{2}.\frac{128}{2145}\)
= \(\frac{192}{715}\)

A =118.75
B=125 -5 .(3.X -1) =25
5.(3.X-1) =100
3.X-1=20
3X =21
X=7

[130 - 3.(5.24 - 52.2) : 23]
= [ 130 - 3.30:23]
= 130 - 11,25
= 118,75
b) 125 -5.(3x-1) = 55:53
125 -5.(3x-1) = 25
5.(3x-1) = 100
3x-1 = 20
3x = 21
x = 7
c) 4x-1 + 40 = 65
4x:4 + 1 = 65
4x:4 = 64
4x = 256 = 44
=> x = 4

CÂU 1
\(5^{n+1}+5^n=750\)
\(=>5^n\cdot5+5^n=750\)
\(=>5^n\cdot\left(5+1\right)=750\)
\(=>5^n\cdot6=750\)
\(=>5^n=750:6\)
\(=>5^n=125\)
\(=>5^n=5^3\)
\(=>n=3\)

(315.4+314.15):316
=(315.4+314.3.5):316
=(315.4+315.5):316
=[315.(4+5)]:316
=[315.9]:316
=315.32:316
=3

Ta có: \(5^{x+2}+5^{x+3}=750\)
\(\Leftrightarrow5^x\cdot\left(5^2+5^3\right)=750\)
\(\Leftrightarrow5^x\cdot150=750\)
\(\Leftrightarrow5^x=5\)
\(\Rightarrow x=1\)
5x+2 + 5x+3 = 750
<=> 5x . 52 + 5x . 53 = 750
<=> 5x (52 + 53) = 750
<=> 5x (25 + 125) = 750
<=> 5x . 150 = 750
<=> 5x = 750 : 150
<=> 5x = 5
<=> x = 1
#Học tốt!!!
~NTTH~
\(750:\left(130-\left(70-65\right)^3+3\right)\)
\(750:\left(130-\left(5^3+3\right)\right)\)
\(750:\left(130-\left(125+3\right)\right)\)
\(750:\left(130-128\right)\)
\(750:2=375\)
Bàn phím mình không viết được ngoặc nhọn,ngoặc vuông nha bạn
\(=750:\left\{130-\left[\left(70-65\right)^3+3\right]\right\}=750:\left\{130-128\right\}=750:2=375\)