12 :{390:[2.5^2-(5^3+7^2.5)]}
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Ta có:
\(12:\left\{390:\left[500-\left(5^3+7^2.5\right)\right]\right\}\)
\(=12:\left\{390:\left[500-125-245\right]\right\}\)
\(=12:\left(390:130\right)\)
\(=12:3=4\)
![](https://rs.olm.vn/images/avt/0.png?1311)
a) x(x+1)=2+4+6+8+...+2500
x(x+1)=(2500+2).1250:2
x(x+1)=1563750
Ta thấy: x và x+1 là 2 số liên tiếp
Mà x(x+1)=1563750=>x=1250;x+1=1251
Vậy x=1250
b) x-3=12:{390:[500-(5^3+7^2.5)]}
x-3=12:[390:(500-254.64)]
x-3=12:(390:245.35)
x-3=12:1.58
x-3=7.54
=>x=10.5
Vậy x=10.5
c) x+3^3.12=3^3.19
=>x=2.46
Vậy x=2.46
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
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1) \(7.4^x=7.4^3\Leftrightarrow4^x=4^3;x=3\)
2) \(\frac{3}{2.5^x}=\frac{3}{2.5^{12}}\Leftrightarrow5^x=5^{12};x=12\)
\(2^x=2.2^8=2^9;x=9\)
4) \(5.3^x=7.3^5-2.3^5\Leftrightarrow5.3^x=3^5.\left(7-2\right)\)
\(\Leftrightarrow3^5.x=3^5.5;x=5\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\frac{2^{12}\cdot5^7+4^6\cdot25^3}{8^5\cdot25^3+\left(2^2\cdot5\right)^6}\)
\(=\frac{2^{12}.5^7+2^{12}\cdot5^6}{2^{15}\cdot5^6+2^{12}\cdot5^6}\)
\(=\frac{2^{12}\cdot5^6\cdot\left(1\cdot5+1\right)}{2^{12}\cdot5^6\cdot\left(2^3\cdot1+1\right)}\)
\(=\frac{6}{9}\)
\(=\frac{2}{3}\)
![](https://rs.olm.vn/images/avt/0.png?1311)