suku ke5=29 dan suku ke 7=41,jumlah S20

[tex]u5 = 29 \\ a + 4b = 29 \\ \\ u7 = 41\\ a + 6b = 41 \\ \\ a + 6b = 41 \\ a + 4b = 29 \\ - - - - - - - \\ 2b = 12 \\ b = 6 \\ \\ a + 4(6) = 29 \\ a= 29 - 24 \\ a = 5[/tex]
[tex]s20 = \frac{20}{2} (2(5) + 19(6)) \\ s20 = 10(10 + 114) \\ s20 = 10(124) \\ s20 = 1240[/tex]