Question

Aflatil pe X: 3X+6X+9X+...+102X=
=3570
Help,pls!!

Answer 1

3x+6x+x+9x+...+102x=3570
3x(1+2+3+..+34)=3570
3x × 24*25/2=3570
3x×1190/2=3570
3x×595=3570
1785x=3570
x=3570:1785
x=2

Answer 2

$\displaystyle 3x+6x+9x+...+102x=3570 \\ \\ 3x(1+2+3+...+34)=3570 \\ \\ 3x \cdot \frac{34(34+1)}{2} =3570 \\ \\ 3x \cdot \frac{34 \cdot 35}{2} =3570 \\ \\ 3x \cdot \frac{1190}{2} =3570 \\ \\ 3x \cdot 595=3570 \\ \\ 1785x=3570 \\ \\ x= \frac{3570}{1785} \Rightarrow \boxed{ x=2}$