
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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