Question

what is logically equivalent to if a line touchs a circle only at one point,then it's tangent

Answer 1

If a line is not tangent to a circle, then it does not touch the circle at only one point,

Answer 2

A logical equivalent of
if A then B
is always
if not B then not A

Answer 3

p -> q equivalent to -pvq, also equivalent to -q->-p