Question

Is this tangent to the circle?

Answer 1

If you are asking about AB, Then in order to be a tangent to the circle the m(A) should be equal to 90 degrees. So we have to test it, if measure of angle "A" is 90 or not. Since the 3 sides lengths were given, I guess they want you to use Pythagorean theorem which says the following:
$hyp^{2}= adj^{2}+opposite^{2}$
hypotenuse in here is the 16 unit length side, the adjacent is AB and  the opposite is the diameter with length of 6.4  unit length.
if $16^{2} = 6.4^{2}+9.6^{2}$ then m(A)= 90 degrees and it will be a tangent.
$16^{2}=256$
$6.4^{2} + 9.6^{2}=40.96+92.16=133.12$ 
so the theorem is not applicable in this situation so the $m(A) \neq 90 degrees$
therefore AB is not a tangent

Answer 2

Hello,

Yes since (2*6.4)²+9.6²=256=16²
Angle A=90°