Answer:
x = 6
Step-by-step explanation:
The ratio of consecutive terms is the same, so we have ...
x/3 = (x +6)/x
x^2 = 3(x +6) . . . . . . multiply by 3x
x^2 -3x -18 = 0 . . . . subtract 3(x+6), simplify
(x -6)(x +3) = 0 . . . . factor
x = 6 . . . . . . . . . the only possible positive value
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Additional comment
The zero product rule tells you that a product will be zero if and only if a factor is zero. That is, the solutions to this equation are values of x that make the factors zero: x = 6, x = -3.
