tolong dijawab yaa nomor 4 saja

Dik : a/U1 : 18, b: -6

a.) U10 = a + (n-1) b
U10 = 18 + (10-1).-6
= 18 + (-54)
= -36

b.) Rumus suku ke - n
Un = a + (n-1) b
= 18 + (n-1) -6
= 18 -6n + 6
= -6n + 24

c.) Sn =
[tex] \frac{n}{2} (2a + (n - 1)b)[/tex]
S16 =
[tex] \frac{16}{2} ((2.18) + (16 - 1) - 6)[/tex]
8 (16+15.-6)
8 (16 - 90)
8 (-74)
-592