Suatu barisan aritmetika dikenali U6 = 18 & U10 = 30. jumlah 16 suku pertama dr barisan tersebut ?
U10 = a + 9b = 30
U6 = a + 5b = 18
…………………………. —
4b = 12
b = 3
a+5b = 18
a+5(3) = 18
a= 18-15 =3
S16 = 16/2 (2a +15b)
= 8 (2.3 + 15.3)
= 8 ( 6 + 45 )
= 8 ( 51 )
= 401