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 please bantu jawab.ma

a)1+3+5+7+9+...+99
a = 1
b = 3 - 1 = 2
n = 100/2 = 50

Sn = 1/2(n)[2a + (n - 1)b]
S50 = 1/2(50)[2(1) + (50 - 1) × 2]
S50 = 25[2 + 49 × 2]
S50 = 25[2 + 98]
S50 = 25 × 100
S50 = 2500

b)1-2+3-4+5-6+7-8+...-100
.....-1.....-1.....-1.......-1........×50

S50 = (-1) × 50 = -50

c)-100-99-98-...-2-1-0+1+2+...+48+49+50

(-50-49-48-...-2-1-0+1+2+...+48+49+50) = 0
sisa barisan -100-99-98-...-53-52-51

a = -100
b = -99-(-100) = -99+100 = 1
n = 50

Sn = 1/2(n)[2a + (n - 1)b]
S50 = 1/2(50)[2(-100) + (50 - 1) × 1]
S50 = 25[-200 + 49 × 1]
S50 = 25[-200 + 49]
S50 = 25 × (-151)
S50 = -3775