If 1/a^2 + a^2 represents the diameter of circle O and 1/a + 2a = 3, which of the following best approximates the circumference of circle O?
Choose the most appropriate option.
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)   16iameter 16 = (1/a)^2 + a^2   = 7 (From (1))   So Radius = 16/2 = 7/2   Circumference = 2*Pi*r   = 2*(22/7)*(7/2)   =16   So the answer should be 16.
<result>D</result>
If 1/a^2 + a^2 represents the diameter of circle O and 1/a + 2a = 3, which of the following best approximates the circumference of circle O?