Answer:
Look below.
Step-by-step explanation:
One property of a cyclic quadrilateral is that the opposite angles are supplementary. Angles ABC and ADC are opposite; therefore, supplementary. We know that angle x is supplementary to angle ABC because they are on the same line. We know that angle y is supplementary to angle ADC because they are on the same line.
ABC + ADC= 180 degrees
ABC + x= 180 degrees
ABC + ADC = ABC + x
- ABC -ABC
ADC= x
ADC+ y= 180 degrees
ADC + ABC= 180 degrees
ADC+y= ADC+ABC
-ADC -ADC
y=ABC
ABC=x ADC=y
ABC + ADC= 180
Property of substitution:
x+y=180
