a. 1+3+5+7+9+...+99 b. 1-2+3-4+5-6+7-8+...-100 c.-100-99-98-...-2-1-0+1+2+...+48+49+50

A.
A= 1
B = 3-1 = 2
Banyak suku :
= 99/2
= 49,5 (50)

S50 :
= n/2 (a + Un)
= 50/2 (1 + 99)
= 25 x 100
= 2500

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

Banyak kali penjumlahan :
= 100/2
= 50

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

C.
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