Question

Jawab dengan pake cara.
1. Tentukan 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. 3+10+17+24 + ... (ditambah 7)
b. 38+33+28+23 + .. (dikurang 5)
c. -5 + (-10) + (-15) + (-20) + ... (ditambah -5)

Answer 2

A. u10 = u1 + (n-1)b = 3 + (10-1) x 7 = 3 + (9x7) = 3 +  63 = 66
s10 (jumlah 10 suku pertama ) = n/2 x (u1 + u10) = 10/2 x ( 3 + 66 ) = 5 x 69 = 345..

b. u10 = u1 + (n-1)b = 38 + (10-1) x -5 = 38 + (9 x (-5) = 38 -45 = -7
s10 = 10/2  x (u1 +u10) = 5 x (38 + (-7)) = 5 x 31 = 155

c. u10 = u1 + (n-1) b = -5 + (10-1) x -5 = -5 + (10-1) x -5 = -5 + (9x-5) = -5 + (-45) = -50
s10 = n/2 x (u1+u10) = 10/2 x (-5 + (-50) = 5 x (-55) = -275

semoga bermanfaat :)