bantu jawab ya besok dikumpulkan

2) hitung S15, jika Un= 2n + 5

jwb :

jika n = 1, maka U1 = 2(1) + 5
U1 = 7
jika n = 15, maka U15 = 2(15) + 5 = 35

S15 = 15/2 ( U1 + U15)
S15 = 15/2 ( 7 + 35)
S15 = 15/2 (42)
S15 = 15 x 21
S15 = 315

37) U7 = 10 dan U13 = 2
maka, U3?

U7 = a + 6b = 10
U13 = a + 12b=2
------------------------ (-)
-6b = 8
b = -(8/6)
jika b= -(8/6), maka a + 6( - 8/6) = 10
a + (-8) = 10
a = 18

U3 = a + 2b
= 18 + 2( -8/6)
= 18 + (- 8/3)
= (54 - 8) / 3
= 46/3

CMIIW ya