Question

determina numarul natural x , stiind ca x+2•x+3•x+...... 10•x=385. Va rog ajutatima

Answer 1

salut!
x+2x+3x+...+10x=385
(10×11:2)×x=385
55x=385
x=385:55
x=7

Answer 2

x+2•x+3•x+...... 10•x=385

x(1+2+3+...+10)=385

$x*\frac{10*11}{2}=385$

$x*5*11=385$

$x*5=385:11$

$x*5=35$

$x=35:5$

$\boxed{x=7}$

SUMA LUI GAUS:

$\boxed{1+2+3+...+n=\frac{n(n+1)}{2} }$

$n\in$|N