Question

Tính A= 1-5+5²-5³+5⁴-5⁵+.....+5⁹⁸-5⁹⁹

Answer 1

Ta có: \(5A=5-5^2+5^3-5^4+...+5^{99}-5^{100}\)

\(\Rightarrow5A+A=6A=1-5^{100}\)

\(\Rightarrow A=\dfrac{1-5^{100}}{6}\)

Mk làm hơi tắt một chút!!! Bn thông cảm nhé!

Answer 2

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