tentukan suku ke U15 dan suku ke U20 pada barisan berikut a.8,17,26,35 b.32,21,10,-1

a ) 8, 17, 26, 35, ...
Un = a + (n-1)b
a = U1 = 8
b = beda = 9

Rumus : Un = 8 + (n-1)9

U15 = 8 + (15-1)9
U15 = 8 + 126
U15 = 134

U20 = 8 + (20-1)9
U20 = 8 + 171
U20 = 179

b ) 32, 21, 10, -1, ...
Un = a + (n-1)b
a = U1 = 32
b = beda = -11

Rumus : Un = 32 + (n-1)-11

U15 = 32 + (15-1)-11
U15 = 32 + (-154)
U15 = -122

U20 = 32 + (20-1)-11
U20 = 32 + (-209)
U20 = -177

Maaf bila ada kesalahan

A) U15 = 134
U20 = 179
B) U15 = -122
U20 = -177