Determine the area of .
Step 1: Find the area of .
Step 2: Find the length of . Use Pythagoras' theorem.
Step 3: Establish that is a right angle.
The converse of Pythagoras' theorem states that if the square of the length of a side is equal to the sum of the squares of the other two sides,
then the angle opposite to this side is a right angle.
Since , and is a right-angled angle.
Step 4: Find the area of .
Step 5: Find the area of quadrilateral .