Jika diketahui deret aritmatika S6=6,S8=24 tentukan suku pertama barisan aritmatika tersebut

S6 = 6/2(2a +5b) = 6a + 15b = 6
S8 = 8/2(2a + 7b) = 8a + 28b = 24

S8 (x3) = 24a + 84b = 72
S6 (x4) = 24a + 60b = 24
====================== --
24b = 48
b = 48/24 = 2

S8 = 8a + 28b = 24
8a + (28x2) = 24
8a = 24 -56 = -32
a = -32/8 = -4

U1 = a = -4