Suku ke-n barisan aritmatika dg un jika u3= -2 dan u6 = 7 tentukan besar suku ke 13

U3 = a + 2b
a + 2b = -2 ••• (1)
U6 = a + 5b
a + 5b = 7 ••• (2)

a + 2b = -2
a + 5b = 7
--------------- -
••• -3b = -9
••••• b = 3

a + 5b = 7
a + 5 (3) = 7
a + 15 = 7
a = -8

Maka,
U13
= a + 12b
= -8 + 12 (3)
= -8 + 36
= 28