Question

tìm x;

1+2+3+...+x=1225

cảm un mọi ngừi

Answer 1

=>x(x+1)/2=1225

=>x(x+1)=2450

=>x=49

Answer 2

1 + 2+ 3 ...... + x = 1225

(1+x).x:2=1225x2

(1+x).x=2450

(1+x).x=49.50

(1+x).x=-49.-50

vậy x thuộc { 50,-49 }