" Life is not a problem to be solved but a reality to be experienced! "
© Copyright 2013 - 2025 KUDO.TIPS - All rights reserved.
b = 9-6 = 3
Sn = n/2 (2a + (n-1)b)
756 = n/2 (12 + 3n - 3)
1512 = n (9 + 3n)
1512 = 9n + 3n²
504 = 3n + n²
n² + 3n - 504 = 0
(n -21)(n+24) = 0
n = 21 atau n = -24
jadi jumlahnya ada 21
b. a = 56
b = -5
Sn = n/2 (112 -5n + 5)
-36 = n/2 (117 - 5n)
-72 = 117 n - 5n²
5n² - 117n - 72 = 0
(5n +3) (n - 24) = 0
n = 24 atau n = -3/5
Banyak suku ada 24
c. a = 10
b = 4
Sn = n/2 (20 + 4n - 4)
640 = n/2 (16 + 4n)
640 = 8n + 2n²
320 = 4n + n²
n² + 4n - 320 = 0
(n + 20)(n - 16) = 0
n = -20 atau n = 16
banyak suku ada 16