Question

                   biet 1^2+2^2+3^2+4^2+...+10^2=385 . Tinh nhanh s=2^2+4^2+6^2+...+20^2

Answer 1

4.385=1540

Answer 2

cmr m=125&,fklmgmni

Answer 3

= 1540 nhé

Answer 4

\(4.385=1540\)

Answer 5

\(S=2^2+4^2+6^2+...+20^2\)

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

Thay \(1^2+2^2+3^2+...+10^2=385\)vào S ta đueọc

\(\Rightarrow S=2^2.385=4.385=1540\)

\(\Rightarrow S=1540\)

Answer 6

đặt T = \(1^2+2^2+...+10^2=385\)

\(\Rightarrow T\times2^2=1^2\times2^2+2^2\times2^2+...+10^2\times2^2=385\times2^2\)

\(\Rightarrow T\times2^2=\left(1.2\right)^2+\left(2.2\right)^2+...\left(10.2\right)^2=385.2^2\)

\(\Rightarrow T\times2^2=\left(2\right)^2+\left(4\right)^2+...+\left(20\right)^2=385.2^2\)

\(\Rightarrow T\times2^2=S=385.2^2\)

\(\Rightarrow S=385\times4\)

                                                                hk tốt

Answer 7

$=2^2+4^2+6^2+...+20^2$

Answer 8

\(S=2^2+4^2+6^2+...+20^2\)

\(\Rightarrow S=2^2.1^2+2^2.2^2+2^2.3^2+...+2^2.10^2\)

\(\Rightarrow S=2^2(1^2+2^2+3^2+...+10^2)\)

\(vì\) \(1^2+2^2+3^2+...+10^2=385\)

\(\Rightarrow S=2^2.385=4.385=1540\)