A builder was given a design plan for a triangular roof as shown. Explain how he knows that △AED ∼ △ACB. Then find AB.

angle AED is congruent to angle ECB and angle ADE is congruent to angle DBC.

Triangle AED is congruent to triangle ACB

AB =  28 feet

Step-by-step explanation:

6/AB = 9/42

42(6) = 9AB

252=9AB

AB=28

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