Question

Tolong jawab ya pakai caranya

jika deret aritmetika U5 = 15 dan U9 + U23 = 96, maka S10 = ........

Answer 1

U5 = a+(5-1)b
15 = a + 4b

U9 + U23 = 96
a+8b + a + 22b = 96
2a + 30b = 96
a + 15b = 48--->U16

cari beda


cari a(suku awal)
U5 = a +(5-1)b
U5 = a +4b
15 = a + (4 x 3)
15 = a + 12
a = 15-12
a = 3

S10 = 10/2 (2x3 + (10-1)3)
S10 = 5(6 + (9 x 3)
S10 = 5 ( 6 + 27)
S10 = 5(33)
S10 = 165