Tính: a) 2^2 + 4^2 + 6^2 + ... + 100^2; b) 40^2 +42^2 + 44^2 + ... +120^2

bài 1 . Tính tổng sau
a) 2^2 +4^ 2 + 6^2 + ........... + 100^2
b) 40^ 2 +42^2 + 44^2 + .........................+120^2 
c) 20^2 + 22^2 + ............ + 48^2 + 50^2
d) 2^2 +4^6+ 6^2 + 8^2 +...........+(2n)^2