Question

Tinh tong sau hop li :

A=2+2 mu 2 + 2 mu 3 + ............+2 mu 100

B=1+3 mu 2 + 3 mu 3 + .......... + 3 mu 2009

C = 4+ 4 mu 2 + 4 mu 3 + ...............+ 4 mu n

Giup minh voi sory may minh ko co dau minh dang can gap lam !!!

Answer 1

Lần sau viết cái đề rõ rõ ra nhs!!!

a) \(A=2+2^2+2^3+................+2^{100}\)

\(\Rightarrow2A=2^2+2^3+2^4+................+2^{100}+2^{101}\)

\(\Rightarrow2A-A=\left(2^2+2^3+..............+2^{100}+2^{101}\right)-\left(2+2^2+............+2^{100}\right)\)

\(\Rightarrow A=2^{101}-2\)

b) \(B=1+3+3^2+..................+3^{2009}\)

\(\Rightarrow3B=3+3^2+3^3+..................+3^{2009}+3^{2010}\)

\(\Rightarrow3B-B=\left(3+3^2+...............+3^{2010}\right)-\left(1+3+3^2+.............+3^{2009}\right)\)

\(\Rightarrow2B=3^{2010}-1\)

\(\Rightarrow B=\dfrac{3^{2010}-1}{2}\)

c) \(C=4+4^2+4^3+................+4^n\)

\(\Rightarrow4C=4^2+4^3+.................+4^n+4^{n+1}\)

\(\Rightarrow4C-C=\left(4^2+4^3+.............+4^n+4^{n+1}\right)-\left(4+4^2+............+4^n\right)\)

\(\Rightarrow3C=4^{n+1}-4\)

\(\Rightarrow C=\dfrac{4^{n+1}-4}{3}\)

Answer 2

\(A=2+2^2+2^3+...+2^{100}\)

\(2A=2^2+2^3+2^4+...+2^{101}\)

\(\Rightarrow2A-A=2^{101}-2\)

\(\Rightarrow A=2^{101}-2\)

Vậy \(A=2^{101}-2\).

\(B=1+3^2+3^3+...+3^{2009}\)

\(3B=3+3^3+3^4+...+3^{2010}\)

\(\Rightarrow3B-B=3^{2010}-7\)

\(\Rightarrow2B=3^{2010}-7\)

\(\Rightarrow B=\dfrac{3^{2010}-7}{2}\)

Vậy \(B=\dfrac{3^{2010}-7}{2}\).

\(C=4+4^2+4^3+...+4^n\)

\(4C=4^2+4^3+4^4+...+4^{n+1}\)

\(\Rightarrow4C-C=4^{n+1}-4\)

\(\Rightarrow3C=4^{n+1}-4\)

\(\Rightarrow C=\dfrac{4^{n+1}-4}{3}\)

Vậy \(C=\dfrac{4^{n+1}-4}{3}\).