Question

giup mk nhe

tinh A=1+5+5^2+....+5^49+5^50

 

Answer 1

Gọi A = 5⁰ + 5¹ + 5² + 5³ +... + 5⁴⁹ + 5⁵⁰. 

Vậy, 5A = 5¹ + 5² + 5³ +... + 5⁵⁰ + 5⁵¹. 

5A - A = 4A = (5¹ + 5² + 5³ +... + 5⁵⁰) + 5⁵¹ - 5⁰ + (5¹ + 5² + 5³ +... + 5⁴⁹ + 5⁵⁰) = 5⁵¹ - 1. 

Tức, A = (5⁵¹ - 1)/4.

Answer 2

Theo đề ta có:

A=1 + 5 + 5^2 + 5^3 +....+5^50

=>5A = 5 + 5^2 +5^3+..........+5^51

=>4A = 5A - A = 5^51 - 1

=>A= 5^51 - 1 / 4