Question

Cho biết $1^2+2^2+3^2+\ldots+10^2=385$ 

Tính $A=3^2+6^2+9^2+\ldots+30^2$.

Answer 1

A = 3² + 6² + 9² + ... + 30²

= (3.1)² + (3.2)² +  (3.3)² + ... + (3.10)²

= 3².(1² + 2² + 3² + ... + 10²)

= 9.385

= 3465

Answer 2

a

Answer 3

Do đó A = 3² + 6² + 9² + ... + 30² = 3465

Answer 4

A = 3² + 6² + 9² + ... + 30² = 385. 3²

A = 3465