Question

Find the sum of the geometric series with the first and last terms as given: a= 4, t6 = 972, r = 3

Answer 1

Also, if you can: what is the sum of the first four terms of a geomtric sequence whose second term is 10 and whose fifth term is -1.25

Answer 2

hmmm

S_n = a1(1-r^n)/1-r

we have a1 which is 4...r which is 3...and n which is 6 (from t6) so the only thing left to do is substitute....

Answer 3

as for your second question you're given a_2 = 10 and T_5 = -1.25

T_5 = (a_2)r)r)r)
T_5 = A_2 r^3
-1.25 = 10r^3

divide both sides by 10...
-0.125 = r^3

cube root both sides...
r = -0.5

can you take it from here??

Answer 4

Im a lil confused, how do i get the terms?