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 A’?
Given that,
U = {x: x is a triangle in the plane}
A = {x: x is a triangle with atleast one angle not equal to 60°}
A’ = U - A = {x : x is a triangle with all angles equal to 60°}
∴ A’ = {x: x is set of all equilateral triangle}.