sum of interior angles theorem

triangle chalkboard exterior hexagon number lines pentagon regular square worksheets polygon octagon equilateral heptagon name sides properties measures color colorful black simple space white calculator degree basic object radians angles students 180 degrees rules teaching three point triangles property learn equation draw science geometric background element school icon concept line formula math vector design theorem interior sum isolated maths mathematics shape education symbol mathematical geometry straight equal abstract euclidean side art graphic class angle flat web teacher