Question

Tolong gimana caranya no 17 & 18
Itu dah ada jawabannya

Answer 1

Deret Geometri

17.a=1/16
r=U2/U1=1/8:(1/16)=1/8x(16/1)=16/8=2
Un=a.r^n-1
16=1/16.2^n-1
2^n-1=16:(1/16)
2^n-1=16x(16/1)
2^n-1=16x16
2^n-1= 256
2^n-1=2^8
n-1=8
n=8+1
n=9

S9=a(r^n-1)/r-1
=1/16(2^9-1)/2-1
=1/16(512-1)/1
=1/16(511)
=1/16x(511)
=511/16 (terbukti)
=31 15/16

Barisan:
1/16,1/8,1/4,1/2,1,2,4,8,16=
1/16+1/8+1/4+1/2=1/16+2/16+4/16+8/16=15/16
1+2+4+8+16=31
Total=31 + 15/16=31 15/16 (terbukti)

18.S5=44
r=-2
Jumlah U4 + U5=?
S5=a(1-r^5)/1-r
44=a(1-(-2)^5)/1-(-2)
44=a(1-(-2^5)/1+2
=a(1-(-32)/3
44x3=a(1+32)
132=a(33)
132=a(33)
132=a(33)
a=132/33
a=4
U4=a.r^n-1
=4.(-2)^4-1
=4.(-2)^3
=4(-8)
=-32

U5=a.r^n-1
=4.(-2)^5-1
=4.(-2)^4
=4.(16)
=64

Barisan:
4,-8,16,-32,64,
U4=-32
U5=64
Total=U4+U5=-32+64=32 (terbukti)

Demikian semoga membantu dan bermanfaat!