Question

in figure AB = 11 cm, BC = 8cm, AD = 3 cm, AC 5cm and A DAC is a right angle.
the area of the quadrilateral ABCD

Answer 1

In "and A DAC is a right angle." I will assume you have a typo and I will just ignore the A in front of DAC

the area of the quadrilateral ABCD = triangle ACD + triangle ABC
= (1/2)(5)(3) + triangle ABC

In triangle ABC, use the cosine law to find angle B
5^2 = 11^2 + 8^2 - 2(11)(8)cos B
..... etc ....

then the area of triangle ABC = (1/2)(11)(8)sin B.
sub back in above and you got it