The first step in his proof should be the givens if they are provided to you. If they aren't when solving a proof, I like to look for stuff that i know is congruent in the pictures and then using theorems and postulates complete the proof.
First step to prove that opposite angle of a quadrilateral in a circle are supplementary is to find the intercepted arc of opposite angles of cyclic quadrilateral.
Step-by-step explanation:
Cyclic quadrilateral:
Cyclic quadrilateral is a quadrilateral which lie on a circle.
As shown in figure, ABCD is a cyclic quadrilateral. First step to show that the opposite angle of a quadrilateral ABCD in a circle are supplementary is to find the intercepted arc of opposite ∠A and ∠C of cyclic quadrilateral.
as shown in figure intercepted are of ∠A is Arc(BCD) and intercepted arc of ∠C is Arc(DAB).
Therefore,
...................(1)
and
...................(2)
We Know that
..............(3)
Put values of Arc(BCD) and Arc(DAB) in equation (3)
.............(4)
Hence,
opposite angles and of cyclic quadrilateral are supplementary.
We can turn 150% into a decimal by moving our decimal point two places to the left, or 1.5. We then multiply 1.5 with 60 as the word "of" in math automatically tells us to do that.