Question

 2² + 3² + 4² + 5² + ... + 20² = ?

Answer 1

2^2+3^2+...+20^2

=2.2+3.3+...+20.20

=1.2+2.3+3.4+...+19.20+1+2+...+20

Gọi A-1.2+...+19.20

3A=1.2.3+2.3.3+...+19.20.3

3A=0.1.2+1.2.3-1.2.3+2.3.4-2.3.4+3.4.5-...+19.20.21-18.19.20

3A=19.20.21

3A=7980

A=2660

B=1+2+...+20

B=20(20+1)/2=210

2^2+...+20^2=2660+210=2870

Answer 2

2^2+3^2+...+20^2

=2.2+3.3+...+20.20

=1.2+2.3+3.4+...+19.20+1+2+...+20

Gọi A-1.2+...+19.20

3A=1.2.3+2.3.3+...+19.20.3

3A=0.1.2+1.2.3-1.2.3+2.3.4-2.3.4+3.4.5-...+19.20.21-18.19.20

3A=19.20.21

3A=7980

A=2660

B=1+2+...+20

B=20(20+1)/2=210

2^2+...+20^2=2660+210=2870

Answer 3

2 mũ 2 + 2 mũ 2 + 2 mũ 3 + 2 mũ 4 + ... + 2 mũ x = 2 mũ 21

Answer 4

Ban kia lam dung roi do 

k tui nha

thanks

Answer 5

2870 nhé bạn à