Homework help plz???

Question

I have just started this chapter about geometric progression and i am havin problems.So plz help me.

So here it is:
the 1st term of a geometric series is 18 and the sum of the first 3 terms is 38, wat is the value of the common ratio?

I need a step by step answer.The 1 who give me a good answer will get 10pts.

Answer 1

18 + 18r + 18r^2 = 38
18r^2 + 18r - 20 = 0
r^2 + r - 20/18 = 0
r^2 + r + 1/4 - 1/4 - 20/18 = 0
(r + 1/2)^2 = (9 + 40)/36
r + 1/2 = ± 7/6

r = 2/3, -5/3

18(1 + 2/3 + 4/9) = 18(9/9 + 6/9 + 4/9) = 18*19/9 = 38
18(1 - 5/3 + 25/9) = 18(9/9 - 15/9 + 25/9) = 18*19/9 = 38

Answer 2

In a geometric progression, each number is the previous one multiplied by a particular constant. For example, in the progression 3, 6, 12, 24 each number is the previous one times 2.

Since you don't know what the constant is, call it R. So your progression is going to be 1, R, R², R³...

You're told that the sum of the first three terms is 38, so 1 + R + R² = 38. This is a simple quadratic equation so you can easily calculate the value of R which is what you are looking for.

Answer 3

dear, this is ur homework,u shuld do it urself