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

Materi Deret Teleskopik

Kelompokkan bilangan sbb
-100 - 99 - .... - 51 + (-50 + 50) + (-49 + 49) + ... + (-1 + 1)
= -100 - 99 - ... - 51
= (-100 - 51) + (-99 - 52) + ... + (-76 - 75) {sebanyak 25 suku}
= 25 × (-151) = -3775

Mapel : Matematika
Kelas : IX SMP
Bab : Barisan dan deret

Pembahasan :
-100 - 99 - 98 - ... + 50

Un = 50
a + (n - 1)b = 50
-100 + (n - 1)1 = 50
-100 + n - 1 = 50
n - 101 = 50
n = 50 + 101
n = 151

Sn = n/2(a + Un)
S151 = 151/2(-100 + 50)
S151 = 151/2(-50)
S151 = -3775