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Answer:
60°
Explanation:
You recognize the ratio of the long side to the short side as 2 : 1, so you know this is the 1 : √3 : 2 "special" triangle that has angles 30°, 60°, 90°. The angle of interest is opposite the longer side, so is the 60° angle.
x° = 60°
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In case you don't remember the "special" 30-60-90 and 45-45-90 right triangles, you can use the relevant trig function:
Cos = Adjacent/Hypotenuse
cos(x°) = 16/32 = 1/2
x° = arccos(1/2)
x° = 60°