the figure AB = 11cm, BC = 8cm, AD = 3cm, AC = 5cm and DAC is a right angle.

Question

The size of ADC;

The size of ACB;

The area of the quadrilateral ABCD.

tan ADC = 5/3
11^2 = 5^2+8^2 - 2*5*8 cos ACB
Now you can figure the areas of the triangles ACD and ACB, and just add them up for the area of ABCD
DAC = 1/2(AD)(AC)

So area ACB =1/2(AB)(BC)sin(ACB)

Answer 1

You just repeated the solution Steve gave you here:

https://www.jiskha.com/questions/1765464/In-the-figure-AB-11cm-BC-8cm-AD-3cm-AC-5cm-and-DAC-is-a-right-angle-The

I don't understand why you re-posted the question.
Just do what he told you to do.

Answer 2

Try to explain .. homework please