Answer
$x=2$
Work Step by Step
In order for a sequence to be geometric, the quotient of all consecutive terms must be constant.
Hence here: $\frac{a_3}{a_2}=\frac{a_2}{a_1}\\\frac{x+2}{x}=\frac{x}{x-1}\\(x+2)(x-1)=x^2\\x^2+x-2=x^2\\x-2=0\\x=2$