1+3+5+7+9+…+99 tolong ya pake cara

a = U1 = 1
b = U2-U1 = 3-1 = 2
Un = 99
maka
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

jadi,
Sn = n/2 . (2a+(n-1).b)

S50
= 50/2 . (2.1+(50-1).2)
= 25 . (2+49.2)
= 25 . (2+98)
= 25 . 100
= 2500