Posted by kingsley on Wednesday, October 5, 2011 at 6:15am.
t(5) = ar^4 = 567
t(3) = ar^2 = 63
divide first equation by the second
ar^4/(ar^2) = 567/63
r^2 = 9
r = ± 3
if r = ±3,
ar^2= 63
a = 7
Since you only want 7 terms, it would probably be faster to just find them and add them up
that is,
7 + 21 + 63 + 189 + 567 + 1701 + 5103 = 7651
or 7 - 21 + 63 - 189 + 567 - 1701 - 5103 = ......
or by formula
if a=7, r= 3
sum(7) = 7(3^7 - 1)/(3-1) = 7651
or if x=-3
sum(7) = 7((-3)^7 - 1)/(-3-1) = .....
Related Questions
Maths - The 5th term of an exponential sequence is 4 and of 2nd term is 35(&...
Maths - The 3rd term of an AP is 10 more than the first term while the fifth ...
maths - in an A.p 6th term is half the 4th term and the 3rd term is 15.How many ...
arithmetic - THE SUM OF THE 2ND AND 5TH TERMS OF AN A.P IS 42. IF THE DIFFERENCE...
arithmetic - the sum of the 3rd and the 4th term is 44 and the sum of the 10th ...
math - The 8th term of ap is 5time the 3rd term, while the 7th term is greater ...
arithmetic - An arithmetic n geometric sequence have the same first term 2.with ...
Arithmetic Progression - In an AP the 6th term is half the 4th term and the 3rd ...
Math - Name School Team Event 3: Logic and Reasoning (with calculators) 5th/6th ...
Math - 1) If the sum of the first n terms of a series is Sn where Sn=2n²-n...
For Further Reading
