barisan aritmetika U5=14 U8=29. tentukan 10 suku pertama

U5 = a + 4b =14
U8 = a + 7b =29
--------------- -
-3b = -15
b = 5
Subsitusi ke pers 1
U5 = a + 4b = 14
a + 20 = 14
a = -6

S20 = 20/2 ((2×(-6) + (19×5))
= 10 ( -12 + 95)
= 10 (83)
= 830