Answer :
Use property of geometric sequence:
[tex]4,x,\frac{1}{36}\\ \\ \frac{x}{4}=\frac{\frac{1}{36}}{x}\\ \\ x^2=4.\frac{1}{36}\\ \\ x^2=\frac{1}{9}\\ \\ x=\pm \frac{1}{9}\\ \\ \boxed{x=\pm \frac{1}{3}}[/tex]
[tex]4,x,\frac{1}{36}\\ \\ \frac{x}{4}=\frac{\frac{1}{36}}{x}\\ \\ x^2=4.\frac{1}{36}\\ \\ x^2=\frac{1}{9}\\ \\ x=\pm \frac{1}{9}\\ \\ \boxed{x=\pm \frac{1}{3}}[/tex]
