added return result for simplify_exponential_function

src/main/py/read_math_function.py

@@ -88,4 +88,5 @@ def simplify_exponential_function(type, function):
     elif new_exponent == 1:
         result = [f"{new_coefficient}x"]
     else:
-        result = [f"{new_coefficient}x^{new_exponent}"]
+        result = [f"{new_coefficient}x^{new_exponent}"]
+    return result