Question

[Citii?]

Tính : T = 3 - 3² + 3³ - 3⁴ + ... - 3²⁰⁰⁰

Answer 1

[Akai Haruma]

Lời giải:
$T=3-3^2+3^3-3^4+....-3^{2000}$

$3T=3^2-3^3+3^4-3^5+...-3^{2001}$

$\Rightarrow T+3T=3-3^{2001}$

$\Rightarrow 4T=3-3^{2001}$

$\Rightarrow T=\frac{3-3^{2001}}{4}$