Question

yimf x 1+2+3+...+x=55

Answer 1

Tổng dãy số đó là :

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

=> \(\frac{\left(x+1\right).x}{2}\)= 55

( x + 1 ) . x = 55 . 2

( x + 1 ) . x = 110

=> x = 10

Vậy x = 10