Ask your own question, for FREE!
Mathematics
OpenStudy (anonymous):

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

OpenStudy (anonymous):

what is ur problem here?

OpenStudy (anonymous):

i mean, where r u stuck?

Parth (parthkohli):

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.

OpenStudy (anonymous):

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

Parth (parthkohli):

And.... \(\Large \color{MidnightBlue}{\Rightarrow a_n = a_1 + (n - 1)d }\) To find the nth term of an arithmetic sequence.

OpenStudy (anonymous):

got it?

OpenStudy (anonymous):

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.

Can't find your answer? Make a FREE account and ask your own questions, OR help others and earn volunteer hours!

Join our real-time social learning platform and learn together with your friends!
Can't find your answer? Make a FREE account and ask your own questions, OR help others and earn volunteer hours!

Join our real-time social learning platform and learn together with your friends!