-100-99-...-2-1-0+1+2+...+48+49+50

A = -100
B = -99 - (-100) = 1
Un = 50
Jumlah suku = 50 + 100 + 1 = 151

S151 :
= n/2 [2a + (n-1) x b]
= 151/2 [2 x -100 + (151-1) x 1
= 75,5 [-200 + 150]
= 75,5 x (-50)
= -3375