Question

Jumlahkan jumlah 10 suku pertama dari barisan bilangan berikut ini:
a) 3+10+17+24+ ....
b) 38+33+28+23+ .....
c) -5 + (-10) + (-15)+ (-20) + ...

Answer 1

A)
a = 3
b = 7
Sn = n/2 (2a + (n-1)b )
S10 = 5 (6 + 9(7) )
S10 = 5(6 + 63)
S10 = 345

b)
a = 38
b = 5
S10 = 5 (76 + 9(5) )
S10 = 5(76 + 45)
S10 = 605

c)
a = -5
b = -5
S10 = 5 (-10 + 9(-5) )
S10 = 5 (-10 - 45)
S10 = 5(-55)
S10 = - 275

Answer 2

A. Diketahui : Barisan 3 + 10 + 17 + 24 + ....
a = 3 b = 7
Ditanya : S10 = .....
Jawab :
Sn = n/2 ( 2 . a + ( n - 1 ) b)
S10 = 10/2 ( 2 . 3 + ( 10 - 1 ) 7 )
= 5 ( 6 + 9 . 7)
= 5 ( 6 + 63 )
= 5 . 69
= 346
b. 38 + 33 + 28 + 23 + .....
a = 38 b = -5
Ditanya : S10 = .... ?
Jawab :
S10 = 10/2 ( 2 . (-38) + ( 10 - 1 ) -5 )
= 5 ( -76 + 9 . (-5) )
= 5 ( -76 + (-45) )
= 5 . (-31)
= -155
c. -5 + (-10) + (-15) + (-20) + (-25) + ....
a = -5 b = -5
Ditanya : S10 = .....?
Jawab :
S10 = 10/2 ( 2 . (-5) + ( 10 - 1 ) -5
= 5 ( -10 + 9 . (-5) )
= 5 ( -10 + (-45)
= 5 . (-35)
= -175
Maaf kalo salah.
Semoga membantu.