No matter what form, what size, a triangle's angles will always add up to 180°

This morning in maths, we investigated the angles of triangles. Firstly, I drew an isosceles triangle and cut out the 3 corners and make connect them to create a straight line. I have learnt that the angles of triangles add up 180° because 180° is a straight line. We repeated this rule but used corners used from different shaped triangles. They too, had angles that added up to 180°