Question

Tìm n sao cho : 7ⁿ + 7^{n + 1} + 7^{n + 2} = 3.19.343

Answer 1

Có: `343=7^3`.

`A=7^n(1+7+49)=3.19.343`

`<=> 7^n.3.19=3.19.7^3`.

`<=> n=3.`

Vậy `n=3`

Answer 2

7ⁿ + 7ⁿ⁺¹ + 7ⁿ⁺² = 3.19.343

7ⁿ.(1 + 7 + 7²) = 19551

7ⁿ.57 = 19551

7ⁿ = 19551 : 57

7ⁿ = 343

7ⁿ = 7³

n = 3