This is about circle theorems. someone asap : (

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