Question

can you check if i got these answers right?
1. Find the sum of the series 5+0+(-5)+...+ (-130)
A. -3500 B. -1750 C. 625 D. -1820
(B is my answer)

2. Find the sixth term of the geometric sequence 1/2, 1/3, 2/9,...
A. 32/2187 B. 32/729 C. 8/81 D. 16/243
(i choose D)

3. Give the first four terms of the geometric sequence for which a_1=-6 and r=4
A. -2,2,6,10
B. -6,-24,-96, -384
C. -6, -3/2, -3/8, -3/32
D. -24,-96,-384,-1536
(i choose A)

4. Which of the following is a geometric mean of 9 and 81?
A. 729 B. 45 C. -27 D. 36
(i choose A)

Answer 1

2.
1/2,1/3,2/9,....
a=1/2
r=(1/3)/(1/2)=1/3*2/1=2/3
tn=ar^(n-1)
n=6
calculate t6

Answer 2

The correct answer will be D (16/243)

Answer 3

correct.

Answer 4

is everything correct then?

Answer 5

first four terms are a1,a1*r,a1*r*r,a1*r*r*r,a1*r*r*r*r

Answer 6

4.
r/9=81/r
r^2=9*81=729
r=27

Answer 7

so -27 would be the best option? (C)

Answer 8

or 729?

Answer 9

-27

Answer 10

r^2=729
r=+-27
Here r=-27

Answer 11

oh ok. are the rest of the problems good then?

Answer 12

3.
-6,-6*4,-6*4*4,-6*4*4*4,-6*4*4*4*4
=-6,-24,-96,-384

Answer 13

1.
not clear with statement.

Answer 14

oh ok. thank you for helping me and for being patient :)