1+2+3+4+5.....+48+49+50 cepat plissss

a = 1
b = 2 - 1 = 1
Un = 50

Un = a + (n - 1)b
50 = 1 + (n - 1)1
50 = 1 + n - 1
50 = n

Sn = n/2 (a + Un)
S50 = 50/2 (1 + 50)
S50 = 25 . 51
S50 =1275

Semoga membantu dan semoga bermanfaat...