Question

Giúp ạaaa!!

Answer 1

Câu 7:

\(A=4+4^2+4^3+...+4^{2003}+4^{2004}\)

=>\(4\cdot A=4^2+4^3+4^4+...+4^{2004}+4^{2005}\)

=>\(4\cdot A-A=4^2+4^3+4^4+...+4^{2004}+4^{2005}-4-4^2-...-4^{2003}-4^{2004}\)

=>\(3\cdot A=4^{2005}-4\)

=>\(3\cdot A+4=4^{2005}=4^{2004}\cdot4⋮4^{2004}\)

Bài 8:

\(A=5+4^2+4^3+...+4^{2020}+4^{2021}\)

=>\(A=1+4+4^2+4^3+...+4^{2020}+4^{2021}\)

=>\(4\cdot A=4+4^2+4^3+4^4+...+4^{2021}+4^{2022}\)

=>\(4\cdot A-A=4+4^2+4^3+...+4^{2021}+4^{2022}-1-4-4^2-...-4^{2020}-4^{2021}\)

=>\(3\cdot A=4^{2022}-1\)

=>\(3\cdot A+1=4^{2022}=4^{2021}\cdot4⋮4^{2021}\)