1. Which of the following sets are empty sets? Justify your answer.
(a) A = {x:x? = 4 and 3x =
=9}.
(b) The set of all triangles in a plane having the sum of their three angles less
than 180.
(a) A = {x:x? = 4 and 3x =
=9}.
(b) The set of all triangles in a plane having the sum of their three angles less
than 180.