SOLUTION: the third term is 12 and the sum of the first two terms is 9. What is the common ratio and first term

Algebra ->  Sequences-and-series -> SOLUTION: the third term is 12 and the sum of the first two terms is 9. What is the common ratio and first term      Log On


   

Question 1140158: the third term is 12 and the sum of the first two terms is 9. What is the common ratio and first term
Answer by josgarithmetic(39618) About Me  (Show Source):
You can put this solution on YOUR website!
TERMS : 
a,  ar,   ar^2

system%28a%2Bar=9%2Car%5E2=12%29

a%281%2Br%29=9
a=9%2F%28r%2B1%29
-
%289%2F%28r%2B1%29%29r%5E2=12
9r%5E2=12r%2B12
3r%5E2=4r%2B4
3r%5E2-4r-4=0,

--
r=%284%2B-+sqrt%2816%2B4%2A3%2A4%29%29%2F6
r=%284%2B-+4%2Asqrt%284%29%29%2F6
r=%284%2B-+8%29%2F6
-
Common Ratio, system%28r=-2%2F3%2COR%2Cr=2%29

Find the "a" which corresponds to each of those using a=9%2F%28r%2B1%29.
.