Question

Tìm n thuộc N biết

c) 1+2+3+...+n = 231

Cám ơn m.b ak!!!!

Answer 1

c, 1+2+3+....+n=231

(n+1).[(n-1):1+1]:2=231

(n+1).n:2=231

(n+1).n=231 . 2 = 462 = 22 . 21

=> n = 21

k mk nha

Answer 2

1+2+3+...+n = 231

(n+1)n:2=231

n(n+1)=231.2

n(n+1)=462

n(n+1)=2.3.7.11

n(n+1)=21.22

=>n=21

k cho mk nha

THANK YOU VERY MUCH