Answer:
60°
Explanation:
The definition of cosine tells you ...
cos(β) = 3/6 = 1/2
β = arccos(1/2) . . . . use the inverse cosine function to find the angle
β = 60°
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The ratio of side lengths in a 30°-60°-90° triangle (one of the "special" triangles), is ...
1 : √3 : 2
The 2 : 1 ratio of longest to shortest side in this right triangle is a clue that the largest acute angle is 60°. It also tells you that x = √3 times the short side length, so is x = 3√3.