Question

1+ 5^2 + 5^4 + 5^6 + ..... + 5^200

tính tổng

 

Answer 1

Đặt \(A=1+5^2+5^4+..........+5^{200}\)

\(5^2A=5^2+5^4+5^6+......+5^{202}\)

\(25A-A=5^{202}-1\)

\(24A=5^{202}-1\)

\(\Rightarrow A=\frac{5^{202}-1}{24}\)

Answer 2

Đặt A = 1 + 5² + 5⁴ + 5⁶ + ... + 5²⁰⁰

5².A = 5² + 5⁴ + 5⁶ + 5⁸ + ... + 5²⁰²

5².A - A = (5² + 5⁴ + 5⁶ + 5⁸ + ... + 5²⁰²) - (1 + 5² + 5⁴ + 5⁶ + ... + 5²⁰⁰)

25.A - A = 5²⁰² - 1

24.A = 5²⁰² - 1

A = 5²⁰² - 1/24

Answer 3

thank mấy pạn nha