Question 1127913
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In a rhombus, the diagonals are perpendicular and bisect each other.  That divides the rhombus into four congruent right triangles.<br>
In each of the triangles, the legs are half the lengths of the diagonal; in this problem the legs are a/2 and (a*sqrt(3))/2.  Since the ratio of the lengths of the legs is 1:sqrt(3), the triangles are 30-60-90 right triangles.<br>
And that makes the angles of the rhombus 60 and 120 degrees.