Renaldo says that parallel lines intersect a circle at opposite ends of the same diameter. If a line is tangent to a circle, then
the radius of the circle is perpendicular to the line at the point of
tangency. Does this fact support Renaldo's conjecture? Explain

Yes

Step-by-step explanation:

Noted that the claim only stands true IF BOTH OF THE LINES ARE TANGENT TO THE CIRCLE. [If one line cut the circle at 2 distinct points, the claim is false]

This can be explained with tangent properties. Consider a circle with radius r, by tangent properties, then the radius of the circle is perpendicular to the line at the point of tangency as stated in the question. Since the two lines are parallel, we can bring back up parallel lines theory, the alternative angles of the two tangent to the circle is equal to 90.

Try to draw a line linking the two points of tangent passing through the radius, it is the diameter of the circle, thus parallel lines intersect a circle at opposite ends of the same diameter.