If 1/a^3 + a^3 represents the diameter of circle O and 1/a + a = 3, which of the following best approximates the circumference of circle O?
Pick one:
A) 28  B) 22  C) 20  D) 16  E) 12
Given that (1/a)+a =3   Square both sides of the equation:   We get,   [(1/a)^2 + a^2 + 2*(1/a)*a] = 9   =&gt; (1/a)^2 + a^2 + 2 = 9   =&gt; (1/a)^2 + a^2 = 7 ----------------- (1)   Diameter D = (1/a)^2 + a^2   = 7 (From (1))   So Radius = D/2 = 7/2   20ircumference = 2*Pi*r   = 2*(22/7)*(7/2)   =20   So the answer should be 20
<result>C</result>
If 1/a^3 + a^3 represents the diameter of circle O and 1/a + a = 3, which of the following best approximates the circumference of circle O?