Why do I use the find function to solve the value of c and x1, but the value of x1 and c can't be found?
You have to assign the result of the "find" command to a variable, like solution:=find(c,x1).
Now solution is a 2x1-vector.
Its more convenient to replace "solution" by a 2x1 vector consisting of the variables c and x1.
Note that Prime won't change the values of the variables c and x1 (guess values) unless you assign them new values as suggested above.
For future questions: Please always attach your worksheet!
Actually there are three possible solutions to this problem:
The one you've found with the given guess values is the middle set.