giup toi vs nha N=1+3^1+3^2+…+3^99 Biet 1^2+2^2+3^2+…+10^2=385 Tinh2^2+4^2+…+20^2 Thank you
giup toi vs nha N=1+3^1+3^2+…+3^99 Biet 1^2+2^2+3^2+…+10^2=385 Tinh2^2+4^2+…+20^2 Thank you
By Natalia
By Natalia
giup toi vs nha N=1+3^1+3^2+…+3^99 Biet 1^2+2^2+3^2+…+10^2=385 Tinh2^2+4^2+…+20^2 Thank you
A=2²+4²+…+20²
⇒A=2².1+2².2²+…+2².10²
⇒A=2²(1²+2²+…+10²)
⇒A=4×385
⇒A=1540
(Học tốt nhé!)
Bạn tham khảo :
$2^2 +4^2+6^2+……….+20^2$
$(1.2)^2+(2.2)^2+(3.2)^2+…+(10.2)^2$
$= 1^2.2^2+2^2.2^2+3^2.2^2+…10^2.2^2$
$= (1^2+2^2+ 3^2+………..10^2).2^2$
$= 385.4$
$= 1540$