it is impossible to solve for c in this example. You need more information.
c
Is angle C 90 degrees or 80 degrees?
a - b = c -(a - b) = -c b - a = -c
a= (+a) or a= (-) b= 2a b= 2a c= (-a) c= (+a)
2a. (a, b and c are all equal.)
A.
A = C = 180 - B = 80 So A + C = 160
by transitive property
A=B , A-B=B-B , A-B =0 B=C , B-B=C-B, 0=C-B So A-B=0 but also C-B=0 A-B=C-B ...add +b ...A-B+B=C-B+B , A=C
Yes.
a = 20 b = 60 c = 100
A=0 b=0 c=0