Step-by-step explanation:
You must set up a proportion, it is called finding the geometric mean.
[tex] \frac{x}{4} = \frac{36}{x} [/tex]
Then, you must cross multiply to get:
[tex] {x}^{2} = 144[/tex]
Then, take the square root
[tex] \sqrt{ {x}^{2} } = \sqrt{144} [/tex]
[tex]x = 12[/tex]
If this answer helped you, I would greatly appreciate the brainliest :D
