a.1-2+3-4+5-4+..-100 adalah..b.-100-99-98-97...-2-1-0+1+2+...48+49+50... jwbny buat besok nih sama pake caranya

A.
1 -2 = -1
3-4 = -1
.. - .. = -1
99-100 = -1

Banyak kali pengurangan :
= 100/2
= 50

Maka hasilnya :
= 50 x (-1)
= -50

B.
A = -100
B = -99 - (-100) = 1
Banyak suku :
= 100 + 1 + 50
= 151

S151 :
= n/2 (a + Un)
= 151/2 (-100 + 50)
= 75,5 x (-50)
= -3775