lengkapilah isian untuk barisan aritmatika berikut! c. u1 = 10 u8 = 73 b = ??? d. u1 = 21 u9 = -3 b = ??? tolong jawabanya ya kawan

c) U1 = 10, U8 = 73, b = ?
Un = a + b(n+1)
U8 = 10 + b(8+1)
73 = 10 + 9b
9b = 73 - 10
9b = 63
b = 63/9
b = 7

d) U1 = 21, U9 = -3, b =??
Un = a + b(n+1)
U9 = 21 + b(9+1)
-3 = 21 + 10b
10b = -3 - 21
10b = -24
b = -24/10
b = -12/5