Answer:
1/2 the area of the quadilateral ABCD
Explanation:
Given a quadilateral ABCD a diagonal BD is drawn.
The area if the triangle formed should always be the half of the area of the quadilateral.
This rule works for quadilateral with similar sides and shape where a diagonal that bisect the shape equally can be drawn
Examples of these quadilateral is
Square
Rectangle
Rhombus