Question

990+991+992+...+1088=

Answer 1

990+991+992+...+1088

S= (1+2+3+...........990+991+992+...+1088)-(1+2+3+..........989)=

1+2+3+...........990+991+992+...+1088)- suma Gauss

S1=[n(n+1)]:2=(1088×1089):2=592416

1+2+3+...........+989)- suma Gauss

S2=[n(n+1)]:2=(989×990):2=489555

S= 4592416 - 489555

S = 102861

Answer 2

990 + 991 + 992 + ... + 1088 =

( 1 + 2 + 3 + ... + 1088 ) - ( 1 + 2 + 3 + ... + 989 ) =

( 1088 × 1089 : 2 ) - ( 989 × 990 : 2 ) =

( 544 × 1089 ) - ( 989 × 495 ) =

592416 - 489555 = 102861