Question

Tìm x:

1+5+9+13+...+x = 4950

 

Answer 1

Ta có: 1+5+9+...+x=4950

⇒\(\dfrac{x.\left(x+1\right)}{2}=4950\)

\(x.\left(x+1\right)=4950.2\)

\(x.\left(x+1\right)=9900\)

⇒x=99