2. pada barisan aritmatika U3 = 13 dan U8 = 48 Tentukan a. suku pertamanya b. beda

Un = a + (n-1)b
U3 = a + 2b = 13
U8 = a + 7b = 48
eliminasi
a + 7b = 48
a + 2b = 13
----------------- _
5b = 35
b = 35/5
b = 7
a + 2(7) = 13
a + 14 = 13
a = 13 - 14
a = -1
a) suku pertama = -1
b) beda = 7

U3 = A + (3-1) B
= A + 2B = 13
U8 = A + (8-1) B
= A + 7B = 48
A + 2B - (A + 7B) = 13 - 48
-5B = -35
B = 7
A + 7×7 = 48
A + 49 = 48
A = -1
Jadi, a. A = -1
b. B = 7