tentukam jumlah n suku pertama dari msing deret aritmatika brkt : a. n=9, a=6 , dan U9= -26 B. n = 20 , a= 4 , U20 = 14 c. n= 33, a= -18 , u33 = -10

sn= n/2 (2a+ n-1 .b)
9= 9/2 (2.6 + 8.20)
=9/2(12+160)
=9/2(172)
=9(86)
=774




b. sn=n/2 (2a+ n-1. b)
= 20/2 (2.4 + 19. 10)
= 20/2(8+190)
=20/2 (270)
=20 .135
=2700


c. sn=n/2 (2a + n-1 .b)
33= 33/2 (2.-18 + 32. 8)
= 33/2 (-36+ 256)
= 33/2 (220)
= 33(110)
=3630