Integrating gives
To compute the integral, substitute 
, so that 
. Then
Since 
for all 
, we can drop the absolute value, so we end up with
Given that 
, we have
so that
The answer is a.0
Concentric means these circles would have the same center, thus, the smaller circle must be inside the bigger circle. Any tangent line to the smaller circle wont be a tangent line to the bigger circle, since that tangent line would intersect at the bigger circle at 2 points. Any tangent line to the big circle will not touch the small circle... so the answer would be 0.
I'm so sorry if this is wrong but it might be 24.
D. The fourth choice is correct.
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