Question

(x+1)+(x+2)+(x+3)+....+(x+100)=99x+5728

Answer 1

100X +(1+2+3+..+100) = 99X +5728
100X +100*101:2=99x+5728
100X-99X= 5728-50*101
X= 5728-5050
X=678

Answer 2

(x +1) +(x +2)+ (x +3)+ ...+ (x +100)=99x+5728
observam  ca  sirul  are  100  de  termeni
dam  factor  comun  si  rezolvam  prin  suma  lui  Gauss
100x+(1+2+3+....+100)=99x+5728
x=5728-100*101/2
x=5728-10100/2
x=5728 - 5050
x=678