The eccentricity of the ellipse x2a2+y2b2=1\frac{x^2}{a^2} + \frac{y^2}{b^2} = 1a2x2+b2y2=1 (a>ba>ba>b) is e=12e = \frac{1}{2}e=21. Find the ratio ba\frac{b}{a}ab.
32\frac{\sqrt{3}}{2}23
12\frac{1}{2}21
22\frac{\sqrt{2}}{2}22
34\frac{3}{4}43