Sum
The sum of three nu,bers in G.P is `39/10` and their product is 1. Find the numbers.
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Solution
Let the number be `a/r`, a and ar.
⇒ `a/r xx a xx ar = 1`
⇒ a3 = 1
⇒ a = 1
Now, `a/r+a+ar=39/10`
⇒ `1/r+1+r=39/10`
⇒ `(1+r+r^2)/r=39/10`
⇒ 10 + 10r + 10r2 = 39r
⇒ 10r2 - 29r + 10 = 0
⇒ 10r2 - 25r - 4r + 10 = 0
⇒ 5r(2r - 5) - 2(2r - 5) = 0
⇒ (2r - 5)(5r - 2) = 0
⇒ r = `5/2` or r = `2/5`
Thus, required terms are :
`a/r, a, ar = 1/(5/2), 1, 1xx5/2` OR `1/(2/5), 1, 1xx2/5`
`=2/5, 1, 5/2` Or `5/2, 1, 2/5`
Concept: Simple Applications - Geometric Progression
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