Answer:
one abbreviation used below triangle = tr
Explanation:
16] as tr ABC is congruent to tr DEF
which means that AB= DE BC=EF AC=DF
acc to given 6 in there in both
8 is there and 9 in other so in which 9 is not there the unknown value there has to be 9 which means x = 9
in triangle, DEF 8 is not there so x-1=8 ---->x=9
17] Similarly in this one 3 and 14 are sides of tr ABC and tr DEF only side is known which is 13 so the unknown side in tr ABC has to be 13
x+1=13 -----> x = 12
in tr, DEF 2 sides are unknown which has to be 3 and 14
so 2 cases will become either x-9= 3 or x-9=14
x-9=3 x-9=14
x=12 x=23
18] In this the given known values of sides of both the tr's is same
so it will become
2x+1=3x-9
9+1 = 3x-2x
-----> x=10
19] in this one only 1 of the known values is same so in tr ABC the unknown has to 28 and the unknown in tr DEF has to be 19
5x-2 = 28 4-y=19
5x= 30 y= 4-19
x=6 y = -15
I hope this helps
I am not confirm whether my answer is correct or not but i tried my best
thanks