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 ${60}^0$,what is A'?

Answer 1

$U=$ Set of all triangles in a plane

$A=$ Set of all triangles with at-least one angle different from ${60}^o$

$A^{\prime }=$ Set of all triangles with no angle different from ${60}^o$

$=$ Set of all triangles with all three angles ${60}^o$

$($ As, in an equilateral triangle, all angles are ${60}^o)$

$=$ Set of all equilateral triangles