Pada barisan aritmatika diketahui U4 =4 dan U8 =11.Tentukan Beda dan U20

un = a + (n-1)b

u4 = a + 3b = 4
u8 = a + 7b = 11
______________ -
             -4b = -7
                b = -7/(-4) = 7/4

subtitusi b ke u4 untuk mendapatkan a
a + 3(7/4) = 4
a + 21/4 = 4
a = 4 - 21/4 = 16/4 - 21/4 = -5/4

u20 = a + 19b = -5/4 + 19(7/4) = -5/4 + 19(7/4) = -5/4 + 133/4) =128/4 = 32

Materi Barisan Aritmetika

U4 = a + 3b = 4
U8 = a + 7b = 11
----------------------- -
-4b = -7
b = 7/4, jadi a + 3(7/4) = 4 => a = 4 - 21/4 = -5/4

U20 = a + 19b = -5/4 + 19(7/4) = 128/4 = 32