Question

ma puteti ajuta????Help!​

Answer 1

Formula pt suma unei progresii geoemtrice

Sn= b1 × (q^n -1)/(q-1).daca q#1

Sn= q×b1 daca q=1

a) S6= 3 × (2^6 -1)/(2-1) =

3×(2^6-1) =

3×63=189

b) 2,5 = 25/10= 5/2

1,5= 15/10 = 3/2

S5 = 5/2 × ((3/2)^5 -1)/(3/2-1) =

5/2 ×(243/32 -1) / (3/2-2/2)=

5/2 ×(243/32-32/32) / 1/2=

5/2 × 2 × 211/32 = 1055/32

c) b3 =b1 ×q^2

q^2 = 2/8

q= V(2/8)

q= V2/2V2 = 1/2

S8= 8 × ((1/2)^8 -1) / (1/2-1) =

8× ((1/256-1) / (1/2-2/2) =

8× -2 × (1/256 - 256/256) =

-16 × (-255/256) =

16×255 = 4080

d) b1 = -9, b2 = -3

q= b2/b1 = -3/-9 = 1/3

S7 = -9 × ((1/3)^7 -1) / (1/3-1) =

-9 × ((1/2187 -1) / (1/3-3/3)=

-9 × (1/2187 -2187/2187) / (-2/3)=

-9 × (-3/2) × (-2186/2187)=

27/2 × (-2186/2187)=

-1093/81