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a, \(-\dfrac{8}{18}-\dfrac{15}{27}=-\dfrac{4}{9}-\dfrac{5}{9}=\dfrac{-4-5}{9}=-\dfrac{9}{9}=-1\)
\(b,\Leftrightarrow x=\dfrac{3}{4}-\dfrac{1}{3}=\dfrac{9}{12}-\dfrac{4}{12}=\dfrac{5}{12}\)
Vậy ...
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1.
b) \(3^x+3^{x+2}=2430\)
\(\Rightarrow3^x.1+3^x.3^2=2430\)
\(\Rightarrow3^x.\left(1+3^2\right)=2430\)
\(\Rightarrow3^x.10=2430\)
\(\Rightarrow3^x=2430:10\)
\(\Rightarrow3^x=243\)
\(\Rightarrow3^x=3^5\)
\(\Rightarrow x=5\)
Vậy \(x=5.\)
c) \(\left(2x-15\right)^5=\left(2x-15\right)^3\)
\(\Rightarrow\left(2x-15\right)^5-\left(2x-15\right)^3=0\)
\(\Rightarrow\left(2x-15\right)^3.\left[\left(2x-15\right)^2-1\right]=0\)
\(\Rightarrow\left[{}\begin{matrix}\left(2x-15\right)^3=0\\\left(2x-15\right)^2-1=0\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}2x-15=0\\\left(2x-15\right)^2=1\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}2x=15\\2x-15=\pm1\end{matrix}\right.\)
\(\Rightarrow\left[{}\begin{matrix}x=15:2\\2x-15=1\\2x-15=-1\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=\frac{15}{2}\\2x=16\\2x=14\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=\frac{15}{2}\\x=8\\x=7\end{matrix}\right.\)
Vậy \(x\in\left\{\frac{15}{2};8;7\right\}.\)
Chúc bạn học tốt!
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\(-\frac{8}{18}-\frac{15}{27}=-\frac{4}{9}-\frac{5}{9}=-\frac{9}{9}=-1\)
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
-1/21 + -1/28 = -4/84 + -3/84 = -7/84 = -1/12
-8/18 + -15/27 = -4/9 + -5/9 = -9/9 = -1
x - 2/5 = 5/7
x = 5/7 + 2/5
x = 25/35 + 14/35
x = 39/35
4/5 - 7/10 + 2/7 = 56/70 - 49/70 + 20/70 = 27/70
2/3 + 7/4 + 1/2 + 3/8 = 16/24 + 42/24 + 12/24 + 9/24 = 79/24
![](https://rs.olm.vn/images/avt/0.png?1311)
=\(\frac{2^{30}3^{16}.5^{50}.7+2^{30}.3^{15}.3^2.11.5^{48}}{11.2^{25}.2^4.5^4.3^{18}.5^{18}.5^{30}-2^{30}.5^{30}.5^{22}.3^{18}}\)
=\(\frac{2^{30}.3^{16}.5^{50}.7+2^{30}.3^{17}.11.5^{48}}{11.2^{29}.5^{52}.3^{18}-2^{30}.5^{52}.3^{18}}\)
=\(\frac{2^{30}.3^{16}.5^{48}.11\left(5^2.7+3\right)}{2^{29}.5^{52}.3^{18}.11\left(1-2\right)}\)
=\(\frac{2.\left(5^2.7+3\right)}{5^4.3^2\left(1-2\right)}\)
=\(\frac{2.178}{5^4.3^2.\left(-1\right)}\)
=\(\frac{356}{-5625}\)
Hk tốt
![](https://rs.olm.vn/images/avt/0.png?1311)
\(-\frac{8}{18}-\frac{15}{27}\)
\(=-\frac{4}{9}-\frac{5}{9}\)
\(=-\frac{9}{9}\)
\(=-1\)
![](https://rs.olm.vn/images/avt/0.png?1311)
a) Ta có:
C = 5/18 + 8/19 - 7/21 + (-10/36 + 11/19 + 1/3) - 5/8
C = 5/18 + 8/19 - 1/3 - 5/18 + 11/19 + 1/3 - 5/8
C = (5/18 - 5/18) + (8/19 + 11/19) - (1/3 - 1/3) - 5/8
C = 1 - 5/8
c = 3/8
b) F = 15/14 - (17/23 - 80/87 + 5/4) + (17/23 - 15/14 + 1/4)
F = 15/14 - 17/23 + 80/87 - 5/4 + 17/23 - 15/14 + 1/4
F = (15/14 - 15/14) - (17/23 - 17/23) + 80/87 - (5/4 - 1/4)
F = 80/87 - 1
F = -7/87
c) G = 1/25 - 4/27 + (-23/27 + -1/25 - 5/43) + 5/43 - 4/7
G = 1/25 - 4/27 - 23/27 - 1/25 - 5/43 + 5/43 - 4/7
G = (1/25 - 1/25) - (4/27 + 23/27) - (5/43 - 5/43) - 4/7
G = -1 - 4/7 = -11/7
\(-\dfrac{8}{18}-\dfrac{15}{27}=-\dfrac{4}{9}-\dfrac{5}{9}=-\dfrac{4}{9}+\left(-\dfrac{5}{9}\right)=-\dfrac{9}{9}=-1\)