a. 1+3+5+7+9+.....+99 pakai cara tolong dijawab yah besok dikumpul

a = U1 = 1

b = U2 - U1
b = 3 - 1
b = 2

Un = 99
a + (n - 1) . b = 99
1 + (n - 1) . 2 = 99
1 + 2n - 2 = 99
2n - 1 = 99
2n = 99 + 1
2n = 100
n = 100 : 2
n = 50

S50 = n/2 . (a + U50)
S50 = 50/2 . (1 + 99)
S50 = 25 . 100
S50 = 2.500