Question

\(t\text{ính}A=1+5+5^2+5^3+...+5^{49}+5^{50}\)

Answer 1

A = 1+5+5²+5³+....+5⁵⁰

5A = 5+5²+5³+5⁴+...+5⁵¹

4A = 5A - A = 5⁵¹ - 1

=> A = \(\frac{5^{51}-1}{4}\)

Answer 2

Ta có: A=1+5+5²+5³+…+5⁴⁹+5⁵⁰

=>5.A=5+5²+5³+5⁴+…+5⁵⁰+5⁵¹

=>5.A-A=5+5²+5³+5⁴+…+5⁵⁰+5⁵¹-1-5-5²-5³-…-5⁴⁹-5⁵⁰

=>4.A=5⁵¹-1

=>\(A=\frac{5^{51}-1}{4}\)