Question:
State in each case whether A ⊂ B or A ⊄ B.
A = {x : x is an isosceles triangle in the plane}, B = {x : x is an equilateral triangle in the same plane}
Solution:
A ⊄ B
Explanation: since all isosceles triangles are not equilateral triangles. Therefore set of isosceles triangle is not contained in the set of equilateral triangle.