Question

(HINT:say x+y+z+w=k)

Answer 1

x+y = w+z (given)

=> x+y+w+z = 360 degree
=> x+y+x+y = 360 degree (x+y = w+z)
=> 2(x+y) = 360 degree
=> x+y = 360/2
=> x+y = 180 degree

=> w+z = 180 degree

Hence, AOB is a line.