Given: Circumscribed ABCD, AB=5,
AD=8, CD=10.
Find: BC

Answer:
BC=7
Step-by-step explanation:
The circle can be circumscribed into the quadrilateral, if the sums of the opposite sides of the quadrilateral are eqaul.
Thus,
[tex]AB+CD=AD+BC,\\ \\8+BC=5+10,\\ \\BC=15-8=7.[/tex]