Points a, b, and c form a triangle. complete the statements to prove that the sum of the interior angles of δabc is 180°.

because a triangle is half of a square even iif it is not a right triangle than the angles have to add up to 180 degrees. because a square is 360 degrees. if the angles are more or less than 180 degrees combines the points witll not touch eachother therfore it will just be a line and not a shape of a triangle.

(not sure if this is what you were looking for but i hope it and if not that i am sorry.)

∠3 ≅ ∠5 and ∠1 ≅ ∠4: alternative angles theorem

m∠1 = m∠4 and m∠3 = m∠5: congruent angles have equal measures.

a 4/6 = 9/12   not proportional

step-by-step explanation:

to find which are not proportional, we can use cross products

if it is true, they are proportional.   if it is not true, they are not proportional.

a 4/6 = 9/12

4* 12 = 6*9

48 = 54

not this is not proportional  

b 2/3 = 12/18  

2* 18 = 3 * 12

36 = 36

this is proportional

c 5/4 = 10/8  

5*8 = 4*10

40 = 40

this is proportional

d 7/5 = 35/25

7*25 = 5 * 35

175 = 175

is proportional