Sn =5n^2 -7 tentukan u3-u5+u7

Kelas 8 Matematika
Bab Barisan dan Deret Bilangan

Sn = 5n² - 7

Un = Sn - S(n - 1)

U3 = S3 - S2
U3 = (5 . 3² - 7) - (5 . 2² - 7)
U3 = (45 - 7) - (20 - 7)
U3 = 25

U5 = S5 - S4
U5 = (5 . 5² - 7) - (5 . 4² - 7)
U5 = (125 - 7) - (80 - 7)
U5 = 45

U7 = S7 - S6
U7 = (5 . 7² - 7) - (5 . 6² - 7)
U7 = (245 - 7) - (180 - 7)
U7 = 65

U3 - U6 + U7
= 25 - 45 + 65
= 45