Q4. These quadrilaterals were convex. What would happen if the quadrilateral is not convex? Consider quadrilateral ABCD. Split it into two triangles and find the sum of the interior angles (Fig 3.7).
Draw a line matching points B and D.Line BD divides ABCD in two triangles . and .
Sum of angles of =
Sum of angles of =
Here,
Adding equation 1 and equation 2,
{ and
i.e. = . }
The sum of the interior angles in a quadrilateral, = .