Question

Bài 2: Cho A= 1^3 + 2^3 + 3^3 +...+ 10^3

tính B= 2^3 + 4^3 + 6^3 +...+ 20^3 theo A

Answer 1

\(B=2^3+4^3+6^3+...+20^3\\=\left(2.1\right)^3+\left(2.2\right)^3+\left(2.3\right)^3+...+\left(2.10\right)^3\\ =2^3.1^3+2^3.2^3+2^3.3^3+...+2^3.10^3\\ =2^3\left(1^3+2^3+3^3+...+10^3\right)\\ =8A\)