if a/b= c/d , express 'c' in term of 'a' and 'x' and express 'd' in term of 'b' and 'x'

Question

where x is variable and x is the set of real numbers.

Answer 1

a/b=c/d => a*d=b*c, or c=(d/b)*a or x*a, where x=d/b.
similarly d=(c/a)*b=x*b, where x=c/a

Answer 2

a = bc/d

d = bc/a

and you would need to give us a function that uses x in relation to the above before i can begin to answer the second part of your question

Answer 3

c=ad-x/b

b=ad-x/c

Answer 4

=You tell us