If line drawn parallel to the base of a isosceles triangle to intersect it's equal sides. prove that the quadrilateral so formed is cyclic

see let triangle be abc with 
<b =<c
let line xy be // to bc which intersect it at x and y
as xy // bc 
so <b +<yxb=180(co ienterior <s of // lines)
<c=<b
therefore
<c+<yxb=180
hence proved pls like it :D
one mr thing ur dp is nice :D