Question

find the area of the quadrilateral ABCD,where AB =9cm, BC =10cm,CD =12cm,Da=11cm

Answer 1

The quadrilateral you were talking about is Trapezoid/Trapezium

$A = \frac{9cm+11cm}{2}10cm\\A= \frac{20cm}{2} 10cm\\A=10cm(10cm)\\A=100cm^2$

Click image for proof.

Answer 2

It is a trapezium
So the formula of finding the area on trapezium in
1/2 *height*[sum of the lengths of the parallel sides]

So to find height use the Pythagoras theorem to get AF(given in my rough digram)


AF = 10.5

So the height is 10.5

Then,put the values


1÷2×10.5×(9+12)
=110.25 cm^2