Square or equilateral triangle inscribed in a circle: side in terms of radius

1. A.
   $\sqrt{\frac{2}{3}}$
2. B.
   $\sqrt{\frac{3}{2}}$
3. C.
   $\frac{3}{\sqrt{2}}$
4. D.
   $\frac{\sqrt{2}}{3}$

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1. A.
   $2y = x$
2. B.
   $2y = \sqrt{3}\,x$
3. C.
   $\sqrt{3}\,y = 2x$
4. D.
   $\sqrt{3}\,y = x$

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1. A.
   $9x^2 = 16y^2$
2. B.
   $27x^2 = 64y^2$
3. C.
   $36x^2 = 49y^2$
4. D.
   $16x^2 = 21y^2$

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