Ta có:S=$2^{2}$ +$4^{2}$ +$6^{2}$ +...+$20^{2}$
=$(1.2)^{2}$ +$(2.2)^{2}$ +$(2.3)^{2}$ +...+$(2.10)^{2}$
=$2^{2}$ .$1^{2}$ +$2^{2}$ .$2^{2}$ +$2^{2}$ .$3^{2}$ +...+$2^{2}$ .$10^{2}$
=$2^{2}$ .($1^{2}$ +$2^{2}$ +$3^{2}$ +...+$10^{2}$ )
=4.385
=1540.
Vậy S=1540.