If one angle of a triangle is 60 degrees, then ithe triangle must be an equilateral triangle.
False
If one angle of a triangle is 60 degrees, it is equilateral if the other two angles are also 60 degrees each.
By constructions we can say that,
If one angle of a triangle is 60 degrees, and the other two are 50 degrees and 70 degrees, then it will be a scalene acute triangle.
If one angle of a triangle is 60 degrees, and the other two are 30 degrees and 90 degrees, then it will be a right angled triangle.
If one angle of a triangle is 60 degrees, and the other two are 100 degrees and 20 degrees, then it will be a scalene obtuse triangle.
So, it is not necessary that if one angle of a triangle is 60 degrees, it is an equilateral triangle.