# I can't finid the answer

1. Mar 5, 2010

### r-soy

Hi

i can't finid the answer

1 - If a1 = 1 and a5 = 100 then r = ?
2 - If a1 = 324 and a9 = 4 then r = ?

"" my answer ""

1 - a5 = a1r^n-1
= 1 (r)^4 = 100
r = (100)^1/4
= 25 but the teacher said mistake .

2 - a9 = a1r^n-1
= 324 (r)^8 = 4
= (4)^1/8 = 0.5 but also the teacher said mistake .

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help me

2. Mar 5, 2010

### Cyosis

Raising something to the power of 1/4 is not the same as dividing by 4 which is what you have done from the looks of it. If you typed it like that into your calculator the calculator would think that 100^1/4=(100^1)/4. Try to type 100^(1/4).

3. Mar 5, 2010

thanks a lot