$3\mathrm{.}43$ The $20-$in$.$ tube $AB$ can slide along a horizontal rod. The ends A and $B$ of the tube are connected

by elastic cords to the fixed point $C.$ For the position corresponding to $x=11in.,$ determine the angle

formed by the two cords $($a$)$ using Eq$.(3\mathrm{.}30),($b$)$ applying the law of cosines to triangle ABC.

$26\mathrm{.}8.$