This task is intended for instruction, providing the students with a chance to experiment with physical models of triangles, gaining spatial intuition by executing reflections.  https://tasks.illustrativemathematics.org/content-standards/tasks/1058

I would start by refreshing students about different types of triangles (isosceles, scalene, equilateral).  

I would then give students tracing paper to trace and label each given triangle.  Once the triangles are traced, they can fold the paper to investigate which lines would be a line of symmetry for each triangle.  

Students can draw extra triangles on the tracing paper to determine any rules for specific types of triangles.  For example: How many lines of symmetry do the given isosceles triangles have? Is that true for all isosceles triangles?

Students can also use the tracing paper to draw other polygons and determine lines of symmetry by folding the paper and looking for a perfect reflection.