Question

Cho A = 3 + 3² + 3³ + 3⁴ + .... + 3⁶⁰

^{giúp mk với ai nhanh mk tick cho}

Answer 1

\(A=3+3^2+........+3^{60}\)

\(3A=3.\left(3+3^2+......+3^{60}\right)\)

\(3A=3^2+3^3+.....+3^{61}\)

\(3A-A=\left(3^2+3^3+.......+3^{61}\right)-\left(3+3^2+.....+3^{60}\right)\)

\(2A=3^{61}-3\)

\(A=\left(3^{61}-3\right):2\)

Answer 2

Ta có: A= 3+3^2+3^3+3^4+...+3^60

\(\Rightarrow\)3A= 3^2+3^3+3^4+...+3^60+3^61 

\(\Rightarrow\)3A-A= (3^2+3^3+3^4+...+3^60+3^61 )- (3+3^2+3^3+3^4+...+3^60)

\(\Rightarrow\)2A= 3^61-3

\(\Rightarrow\)A= \(\frac{3^{61}-3}{2}\)

NHớ k cho mk nhá