Question

B=1+5+5 mũ 2 +5 mũ 3 + ... + 5 mũ 150

Answer 1

B=1+5+5² +5³+ ... + 5¹⁵⁰

⇒5B-B=(5+5²+...5¹⁵⁰)-(1+5+...+5¹⁵⁰)

⇒4B=5¹⁵¹-1

⇒B=\(\dfrac{5^{151}-1}{4}\)

 

Answer 2

\(B=1+5+5^2+5^3+...+5^{150}\)

\(\Rightarrow5B=5+5^2+5^3+...+5^{151}\)

\(\Rightarrow5B-B=5^{151}-1\)

\(\Rightarrow4B=5^{151}-1\)

\(\Rightarrow B=\dfrac{5^{151}-1}{4}\)

Vậy \(B=\dfrac{5^{151}-1}{4}\)