Question

Rút gọn A = 1 + 5 + 5² + 5³ + .... + 5⁴⁹ + 5⁵⁰

Answer 1

Ta có :A = 1 + 5 + 5² + 5³ + .... + 5⁴⁹ + 5⁵⁰

=> 5A = 5 + 5² + 5³ + .... + 5⁵⁰ + 5⁵¹

=> 5A - A = 5⁵¹ - 1 

=> 4A = 5⁵¹ - 1

=> A = \(\frac{5^{51}-1}{4}\)

Answer 2

A=\(5^{51}\)\(-5^0\)

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Answer 3

A=1+5+5²+5³+...+5⁴⁹+5⁵⁰

5A=5.(1+5+5²+5³+...+5⁵⁰)

5A=5+5²+5³+5⁴+...+5⁵¹

5A-A=(5+5²+5³+...+5⁵¹)-(1+5+5²+...+5⁵⁰)

 4A=5⁵¹-1

  A=\(\frac{5^{50}-1}{4}\)