Question

I need help with these questions . please help me :/


What is the sum of an 8-term geometric series if the first term is 15 and the last term is -4,199,040? (3 points)
Answer

-3,599,175

-3,359,230

-3,119,285

-2,879,340


What is the sum of an 8-term geometric series if the first term is -11, the last term is 859,375, and the common ratio is -5? (3 points)
Answer

-143,231

-36,047

144,177

716,144


What is the 25th term of the arithmetic sequence 9, 15, 21, ? (3 points)
Answer

151

152

153

154

Answer 1

what is ur problem here?

Answer 2

i mean, where r u stuck?

Answer 3

Sum of a geometric series is:

\(\Large \color{MidnightBlue}{\Rightarrow a {1 - r^n \over 1 - r} }\)
a is the first term.
n is the number of terms
r is the common ratio.

Answer 4

Lets assume a common ratio r
if the first term is 15
the nth term is 15 x r^(n-1)
hence eighth term is 15 x r^7

Compute r from here. Use Parth's formula

Answer 5

And....

\(\Large \color{MidnightBlue}{\Rightarrow a_n = a_1 + (n - 1)d }\)

To find the nth term of an arithmetic sequence.

Answer 6

got it?

Answer 7

question 3 is fairly easy. just find the common difference and use the arithmetic sequence formula to find the equation for finding the nth term. Then just plug in 25 in that equation.