If you don't have Excel 2013, you can fake the FORMULATEXT function with a short function in Visual Basic. I did use the question that douglaslps referenced to return it as a value instead of just the string. (Very neat answer, that one.) In cell C1, you'd use the formula:
and you'd put this function in the workbook's modules somewhere:
Public Function CombineFormulas(RangeToCombine As Range, Operator As String)
'Input: Range of cells and an operator to use when combining their formulas
'Output: String of the combined formulas
Dim cell As Range
Dim s As String
s = "="
For Each cell In RangeToCombine.Cells
If Len(s) > 1 Then s = s & Operator
s = s & "(" & Mid(cell.Formula, 2, Len(cell.Formula)) & ")"
CombineFormulas = Evaluate(s)