Tentukan hasil dari (tanpa menghitung satu persatu) 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][
1+3+5+7+...+99
n = (99-1)/2 + 1 = 50
S50 = (n/2)(a + Un)
S50 = (50/2)(1 + 99) = 2500

b][
(1-2) + (3-4) + ... + (99-100)
A + B = 1 - 2 + 3 - 4 + 5 - ... + 99 - 100

Ada 2 deret :
A = 1 + 3 + 5 + ... + 99
n = 50
Sn = (n/2)(a + Un)
A = S50 = (50/2)(1 + 99)
S50 = 2500

B = -2 - 4 - 6 - ... - 100
n = 50
B = S50 = (50/2)(-2 - 100)
S50 = -2550

A + B
= 2500 + (-2550)
= -50

Cara lain
(1-2)+(3-4)+...+(99-100) = (-1) × 100/2 = -50

c][
-100-99-...-2-1+0+1+2+...+50
= -100-99-...-51
n = 50
S50 = (50/2)(-100-51) = -3775