Question

Mọi người giúp mình nha.

Rút gọn biểu thức: A= 1+3+3²+3³+.....+3 mũ6

Answer 1

\(3A=3+3^2+3^3+...+3^7\)

\(3A-A=3+3^2+3^3+...+3^7-1-3-3^2-...-3^6\)

\(2A=3^7-1\)

\(A=\frac{3^7-1}{2}\)

Chúc em học tốt^^

Answer 2

\(A=1+3+3^2+...+3^6\)

\(3A=3+3^2+3^3+...+3^7\)

\(3A-A=\left(3+3^2+3^3+...+3^7\right)-\left(1+3+3^2+...+3^6\right)\)

\(2A=3^7-1=2186\)

\(A=1093\)

Answer 3

cảm mơn ạ

Answer 4

Có:

  A=1+3+3²+3³+.....+3⁶

3A=3+3²+3³+3⁴+...+3⁷

2A=3+3²+3³+3⁴+...+3^{7 -} 1+3+3²+3³+.....+3⁶

2A=3⁷-1

=>A=(3⁷-1):2