Answer:
(7) AB is a tangent , (8) AB is not a tangent
Explanation:
the angle between a tangent and the radius is 90°
if AB is a tangent then Δ ABC is right with hypotenuse AC
using Pythagoras' identity
the square on the hypotenuse of a right triangle is equal to the sum of the squares on the other 2 sides.
if AC² = AB² + BC² , then AB is a tangent to the circle
(7)
AC² = 34² = 1156
AB² + BC² = 30² + 16² = 900 + 256 = 1156
since AC² = AB² + BC² , then AB is a tangent to the circle
(8)
AC² = 28² = 784
AB² + BC² = 21² + 20² = 441 + 400 = 841
since AC² ≠ AB² + BC² , then AB is not a tangent to the circle