Answer:
x = 3√3
Explanation:
You want the middle-length side of a 30°-60°-90° triangle whose short side is 3.
Special triangles
There are two "special" triangles in trigonometry. The ratios of their side lengths are used in many algebra, trig, and geometry problems.
30°-60°-90° triangle has sides in the ratios 1 : √3 : 2
45°-45°-90° isosceles right triangle has sides in the ratios 1 : 1 :√2
Application
The triangle shown in this problem is a 30°-60°-90° right triangle with a short side of length 3. You want the middle-length side (x), which the above tells us is √3 times the length of the short side.
x = 3√3
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Additional comment
You can use the trig relation ...
Tan = Opposite/Adjacent ⇒ Adjacent = Opposite/Tan
For this triangle, this means ...
x = 3/tan(30°)
x = 3/(1/√3) = 3√3
A suitable calculator can show this in the desired format.