Question

Let U be the set of all triangles in a plane. If A is the set of all triangles with at least one angle different from 60°, what is ?

Answer 1

U=set of all triangles

Thus,

U={ x:x is a triangle }

A=set of all triangles with atleast one angle different from 60° .

Therefore,

, A ′ =U−A ={ x:x is a triangle }−{ x:x is a triangle with atleast one angle different from 60° } ={ x:x is a triangle and no angles different from 60° } ={ x:x is a triangle with all angles as 60° }

Thus, A ′ is a set of all theequilateral triangles.