Answer:
Aight mate
Explanation:
So every triangles angles will add up to 180 degrees no matter the triangle. Now a circle is 360 and a line is 180. Look at the line that A and C are on this line equals 180. So angle c and d added together make 180 and angles a b and c added together make 180. so if a+b+c = c+d then a+b=c. I hope thaqtmakes sense.