tentukan suku ke 15 dan jumlah suku ke 15 dari soal 1,3,5,7,9

beda = 2
a = U1 = 1
U15 = a + (15 - 1)b = 1 + 14 x 2 = 29
S15 = 1/2 x n (1 + U15) = 1/2 x 15 (1 + 29) = 225

u1 = 1
b = 2
u15 = 1 + (14)2 = 29
s15 = 15/2 ( 2.1+(14)2)
= 15/2 ( 30) = 15 x 15 = 225