1 -2+3-4+5-6+7-8+....-100

Bab Pola Bilangan
Matematika SMP Kelas VII

1 - 2 + 3 - 4 + ...+ 99 - 100 = ?
hanya berlaku pada bilangan asli berurutan
seluruh = n/2
seluruh = -100/2
seluruh = -50

1-2+3-4+5-6+7-8+...-100
a = (1-2) = -1
b = (3-4)-(1-2) = -1 - (-1) = -1 + 1 = 0
n = 100/2 = 50

Sn = 1/2(n)[2a + (n - 1)b]
S50 = 1/2(50)[2(-1) + (50 - 1)× 0]
S50 = 25[-2 + 49(0)]
S50 = 25[-2 + 0]
S50 = 25(-2)
S50 = -50