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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