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+) \(24+\left(x-6\right)=135\)
\(\Rightarrow x-6=135-24=111\)
\(\Rightarrow x=111+6=117\)
+) \(2019-2\cdot\left(3x-2\right)=19\)
\(\Rightarrow2\cdot\left(3x-2\right)=2019-19=2000\)
\(\Rightarrow3x-2=2000:2=1000\)
\(\Rightarrow3x=1000+2=1002\)
\(\Rightarrow x=1002:3\)
\(\Rightarrow x=334\)
+) \(3^x+3^{x+1}=324\)
\(\Rightarrow3^x+3^x\cdot3=324\)
\(\Rightarrow3^x\cdot\left(1+3\right)=324\)
\(\Rightarrow3^x\cdot4=324\) \(\Rightarrow3^x=324:4=81\)
\(\Rightarrow3^x=3^4\) \(\Rightarrow x=4\)
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a.
\(A=5.\left(2^2\right)^{15}.\left(3^2\right)^9-2^2.3^{20}.\left(2^3\right)^9=5.2^{30}.3^{18}-2^2.3^{20}.2^{27}\)
\(=5.2^{30}.3^{18}-3^{20}.2^{29}=2^{29}.3^{18}.\left(5.2-3^2\right)=2^{29}.3^{18}\)
\(B=5.2^9.\left(2.3\right)^{19}-7.2^{29}.\left(3^3\right)^6=5.2^9.2^{19}.3^{19}-7.2^{29}.3^{18}=5.2^{28}.3^{19}-7.2^{29}.3^{18}\)
\(=2^{28}.3^{18}.\left(5.3-7.2\right)=2^{28}.3^{18}\)
=> \(A:B=\left(2^{29}.3^{18}\right):\left(2^{28}.3^{18}\right)=\frac{\left(2^{29}.3^{18}\right)}{\left(2^{28}.3^{18}\right)}=2\)
b. kiểm tra lại đề bài nhé
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\(\frac{1}{2}+\frac{5}{6}+\frac{11}{12}+\frac{19}{20}+...+\frac{89}{90}\)
\(=1-\frac{1}{2}+1-\frac{1}{6}+1-\frac{1}{12}+1-\frac{1}{20}+...+1-\frac{1}{90}\)
\(=9-\left(\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+...+\frac{1}{90}\right)\)
\(=9-\left(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+...+\frac{1}{9.10}\right)\)
\(=9-\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+....+\frac{1}{9}-\frac{1}{10}\right)\)
\(=9-\left(1-\frac{1}{10}\right)\)
\(=9-\frac{9}{10}=\frac{81}{10}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
Có phải ý bn là thế này ko:
\(\frac{19^{100}+19^{96}+19^{92}+...+19^4+1}{19^{102}+19^{100}+19^{98}+...+19^2+1}\)
\(9^{12}.19-3^{24}.19\\ =\left(3^2\right)^{12}.19-3^{24}.19\\ =3^{24}.19-3^{24}.19=0\)
ét o ét