Question

Cho A=6⁰ +6¹+ ...+6⁵ . Tìm x sao cho 5.A+1= 6^x​​​

Answer 1

6A = 6 + 6² + ....+ 6⁶

6A - A  = (6 - 6) + (6² - 6²) + .... + (6⁵ - 6⁵) + 6⁶ - 1

5A = 6⁶ - 1

\(A=\frac{6^6-1}{5}\)

5A + 1 = 6⁶ - 1 + 1 = 6⁶

Vậy x = 6

Answer 2

A=1+6+...+6⁵

6A=6+6²+...+6⁶

6A+1=1+6+6²+...+6⁶=A+6⁶

6A-A=6⁶-1

5A=6⁶-1

5A+1=6⁶-1+1=6⁶-(1-1)=6⁶

mà 5A+1=6^x

nên x=6

Vậy x=6