Ta có :
\(S=\left(0,25\right)^2+\left(0,5\right)^2+...+\left(2,5\right)^2\)

\(\Rightarrow4S=2^2.\left(0,25\right)^2+2^2.\left(0,5\right)^2+.....+2^2.\left(2,5\right)^2\)

\(\Rightarrow4S=1^2+2^2+....+10^2\)

\(\Rightarrow4S=385\)

\(\Rightarrow S=\frac{385}{4}\)

\(a,2^2+4^2+6^2+...+20^2\)

\(=1^2.2^2+2^2.2^2+3^2.2^2+...+10^2.2^2\)

\(=\left(1^2+2^2+3^2+...+10^2\right).2^2\)

\(=385.4\)

\(=1540\)

\(b,\left(0.25\right)^2+\left(0.5\right)^2+...+\left(2.5\right)^2\)

\(=1^2.0,25^2+2^2.0,25^2+...+10^2.0,25^2\)

\(=\left(1^2+2^2+...+10^2\right).0,25^2\)

\(=385.0.0625\)

\(=24.0625\)

a/ Có tự ghi lại đề

= ((2+8)+(4+6)+10+(12+18)+(14+16)+20))^2

= ((10+10+10+30+30+20))^2

=(110)^2

=100^2+10^2

=10000+100

=10100

Đạt A=2^2+4^2+6^2+...+20^2

      A=2^2X(1^2+2^2+3^2+...+10^2) (1)

Mà 1^2+2^2+3^2+...+10^2=385(2)

Thay (2) vào (1), có: A=2^2x385

                              A=4X385=1540

Vậy 2^2+4^2+6^2+...+20^2 = 1540

  A=2^2X(1^2+2^2+3^2+...+10^2) (1)

Mà 1^2+2^2+3^2+...+10^2=385(2)

Thay (2) vào (1), có: A=2^2x385

                              A=4X385=1540

Vậy 2^2+4^2+6^2+...+20^2 = 1540

\(\text{a)}25\%-\frac{3}{2}+0,5.\frac{12}{5}\)

\(=\frac{1}{4}-\frac{3}{2}+\frac{1}{2}.\frac{12}{5}\)

\(=-\frac{5}{8}+\frac{6}{5}\)

\(=-\frac{25}{40}+\frac{48}{40}\)

\(=\frac{23}{40}\)

\(b)0,25.\frac{7}{3}.30.\text{ }0,5.\frac{8}{45}\)

\(=\frac{1}{4}.\frac{7}{3}.30.\frac{1}{2}.\frac{8}{45}\)

\(=\frac{7}{12}.(30.\frac{8}{90})\)

\(=\frac{7}{12}.\frac{8}{3}\)

\(=\frac{14}{9}\)

\(c)\frac{9}{23}.\frac{5}{8}+\frac{9}{23}.\frac{3}{8}-\frac{9}{23}\)

\(=\frac{9}{23}.\left(\frac{5}{8}+\frac{3}{8}-1\right)\)

\(=\frac{9}{23}.0\)

\(=0\)

Ta có \(2^2+4^2+...+20^2=2^2\left(1^2+2^2+...+10^2\right)=2^2.385=1540\).

A. 1155 nha bạn 

Lời giải:
$=27\times 2+12,44\times 4+17,56\times 4+23\times 2$

$=2\times (27+23)+4\times (12,44+17,56)$

$=2\times 50+4\times 30$

$=100+120=220$