Question

prove that in a quadrilateral the sum of all angles are 360degree

Answer 1

For any quadrilateral, we can draw a diagonal line to divide it into two triangles. Each triangle has an angle sum of 180 degrees. Therefore the total angle sum of the quadrilateral is 360 degrees. The exterior angles of a shape are the angles you get if you extend the sides.
angle sum property of a quadrilateral=360°