Question

Tolong bantuanya ya ...makasih udah jawab kalau bisa pakai cara

Answer 1

A= 5 disubstitusikan ke
Un = a.rpangkatn-1
U4 = 5.r pangkat 4-1=40
U4 = r pangkat 3 =40/5
U4 = r =2

Sn = a(rpangkat n -1)/r-1
S6 = 5(2pangkat6 -1)/2-1
S6 = 5(64-1)/1
S6 = 5(63)
S6 = 315....c

Answer 2

1.)
u1 = a = 5
u4 = ar^3
40 = 5r^3
r^3 = 40/5
r^3 = 8
r = 2
s6 = a(r^n - 1)/r - 1
     = 5(2^6 - 1)/2 - 1
     = 5(64 - 1)/1
     = 5x63
     = 315

2.)
u7 = a+(7-1)b
26 = a+6b....1
u4 = a+(4-1)b
14 = a+3b....2

eliminasi 1 dan 2
a+6b = 26
a+3b = 14
________ -
    3b = 12
      b = 4
a+3(4) = 14
a+12   = 14
a         = 2

u30= 2+(30-1)4 = 118
u35= 2+(35-1)4 = 138
s15= 15/2 (2x2 +(15-1)4)
      = 15/2 x 60 = 450
s20= 20/2 (2x2 +(20-1)4)
      = 10 x 80 = 800