Question

Tìm số tư nhiên biết 

1+2+3+...+x=500500

Answer 1

\(1+2+3+....+x=500500\)

\(\Rightarrow\frac{x.\left(x+1\right)}{2}=500500\)

\(\Rightarrow\left(x+1\right).x=1001000=1000.1001\)

\(\Leftrightarrow\left(x+1\right).x=\left(1000+1\right).1000\)

\(\Leftrightarrow x=1000\)

Vậy \(x=1000\)

Answer 2

\(1+2+3+...+x=500500\)

\(\Rightarrow\frac{x\left(x+1\right)}{2}=500500\)

\(\Rightarrow x\left(x+1\right)=1001000\)

\(\Rightarrow x\left(x+1\right)=1000.1001\)

\(\Rightarrow x=1000\)

Vậy \(x=1000\)

Answer 3

Tìm số tự nhiên biết

1+2+3+...+x=500500

Đặt A=1+2+3+...+x

A số số hạng (x-1)\(\div\)1+1 =x(số hạng)

A=(x+1).x\(\div\)2

\(\Rightarrow\)(x+1).x\(\div\)2=500500

\(\Rightarrow\)(x+1).x=500500.2

=1001000

\(\Rightarrow\)(x+1).x=100100.10

\(\Rightarrow\) x=10

Answer 4

1+2+3+...+x=500500

Đặt A 1+2+3+...+x

A= (x+1).x\(\div\)2

\(\Rightarrow\)(x+1).x\(\div\)2=500500

\(\Rightarrow\)(x+1).x=500500.2

x=1001000

\(\Rightarrow\)(x+1).x=1001.1000

\(\Rightarrow\) x=1000