SOLUTION: Please help me solve this qeustion, The second term of a g.p is 6 and the 4th term is 24 find the sum of the first 4 term

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Question 783381: Please help me solve this qeustion, The second term of a g.p is 6 and the 4th term is 24 find the sum of the first 4 term
Answer by KMST(5328) About Me  (Show Source):
You can put this solution on YOUR website!
b%5B1%5D = first term of the geometric progression
r = common ratio of the geometric progression
b%5Bn%5D=b%5B1%5D%2Ar%5E%28n-1%29 = nth term of the geometric progression

--> --> system%28b%5B1%5D%2Ar=6%2Cr=sqrt%284%29=2%29 --> system%28b%5B1%5D%2A2=6%2Cr=2%29 --> system%28b%5B1%5D=6%2F2=3%2Cr=2%29

b%5B3%5D=3%2A2%5E%283-1%29=3%2A2%5E2=3%2A4=12
The sum of the first four terms is
3%2B6%2B12%2B24=highlight%2845%29

If we wanted to get more complicated we could use a formula for the sum of the first n terms, S%5Bn%5D.
S%5Bn%5D=b%5B1%5D%2A%28r%5En-1%29%2F%28r-1%29
S%5B4%5D=3%2A%282%5E4-1%29%2F%282-1%29=3%2A%2816-1%29%2F1=3%2A15=highlight%2845%29