The magnitude of the resultant vector shown is

  2√3

Step-by-step explanation:

You recognize this as a 30°-60°-90° triangle, so you know the hypotenuse (R) is twice the length of the shortest side (√3).

The magnitude of R is 2√3.

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In case you haven't memorized the ratios for a 30°-60°-90° triangle, you can use trigonometry and the fact that ...

  Sin = Opposite/Hypotenuse

  sin(30°) = √3/R

  R = √3/sin(30°) = √3/(1/2) = 2√3

Of course, doing this on your calculator will give a numerical answer, which you may not want.