Question

\(1+2+3+...+x=45\)

Answer 1

\(1+2+3+4+5+6+7+8+9=45\)

\(x=9\)

Answer 2

1 + 2 + 3 ....... + x  = 45

x = 45 - 1 - 2- 3 ....

x =9

nhé !

Answer 3

\(1+2+3+....+x=45\)

\(\Rightarrow\frac{x\left(x+1\right)}{2}=45\)

\(\Rightarrow x\left(x+1\right)=45.2\)

\(\Rightarrow x\left(x+1\right)=90=9.10\)

\(\Rightarrow x=9\)

Answer 4

Giảng dể hiểu thôi

Answer 5

hoc ngu qua 

k minh nha