Question

1.Tính :

A = 2² + 4² + 6² + ... + 100²

A = 1² + 3² + 5² + ... + 99²

Answer 1

A= (2+4+6+...+100)^2

A=2550^2

A=6502500

bài còn lại cũng vậy

Answer 2

A = 2² + 4² + 6² + ... 98²+ 100²

=2² ( 1² + 2² +3²+ ... + 49²+50²)

=\(4.\dfrac{50.\left(50+1\right)\left(2.50+1\right)}{6}=171700\)

Answer 3

Bài cuối :

\(A=1^2+3^2+5^2+7^2+99^2\)

\(A=1+2^2+3^2+4^2+5^2+...+99^2\)

\(A=1+2^2+3^2+4^2+5^2+...+99^2\)

\(A=1+2.\left(3-1\right)+3.\left(4-1\right)+...+99.\left(100-1\right)\)

\(A=\left(2.3+3.4+...+99.100\right)-\left(1+2+3+...+99\right)\)

\(A=\dfrac{99.100.101}{3}-\dfrac{99.\left(99+1\right)}{2}\)

\(A=333300-4950\)

\(A=328350\)