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1.
a) \(3^4\times3^5\times3^6=3^{4+5+6}=3^{15}\)
b) \(5^2\times5^4\times5^5\times25=5^2\times5^4\times5^5\times5^2=5^{2+4+5+2}=5^{13}\)
c) \(10^8\div10^3=10^{8-3}=10^5\)
d) \(a^7\div a^2=a^{7-2}=a^5\)
2.
\(987=900+80+7\\ =9\times100+8\times10+7\\ =9\times10^2+8\times10^1+7\times10^0\)
\(2021=2000+20+1\\ =2\times1000+2\times10+1\times1\\ =2\times10^3+2\times10^1+1\times10^0\)
\(abcde=a\times10000+b\times1000+c\times100+d\times10+e\times1\\ =a\times10^4+b\times10^3+c\times10^2+d\times10^1+e\times10^0\)
\(2S=2^3+2^3+2^4+...+2^{21}\\ S=2^{21}+2^3-2^2-2^2=2^{21}+8-4-4=2^{21}\)
M=2^2+2^2+2^3+...+2^2022
=>2M=2^3+2^3+2^4+...+2^2022+2^2023
=>2M-M=2^2023+2^2022+...+2^4+2^3+2^3-2^2022-...-2^3-2^2-2^2
=>M=2^2023+2^3-2^2-2^2
=>M=2^2023
8=2^3 ; 20=20^1 ; 60=60^1 ; 90=90^1
16=2^4 ; 27=3^3 ; 81=3^4 ; 100=10^2
\(M=4+2^2+2^3+...+2^{2022}\)
\(2M=8+2^3+2^4+...+2^{2023}\)
=>\(2M-M=2^{2023}+8-2^2-4=2^{2023}\)
=>\(M=2^{2023}\)
Ta coi \(B=2^1+2^2+2^3+...+2^{100}\)
\(\Rightarrow A=B+2\)
Ta có:
\(B=2^1+2^2+2^3+...+2^{100}\)
\(\Rightarrow2B=\left(2^1+2^2+2^3+...+2^{100}\right).2\)
\(=2^2+2^3+2^4+...+2^{101}\)
\(\Rightarrow B=2B-B=\left(2^2+2^3+2^4+...+2^{101}\right)-\left(2^1+2^2+2^3+...+2^{100}\right)\)
\(=2^{101}-2\)
\(\Rightarrow A=2^{101}-2+2=2^{101}\)