In a parallelogram, the diagonals bisect each other. This means that the length of segment \( KN \) is equal to the length of segment \( NM \). Given the lengths:
- \( KM = 5x + 1 \)
- \( NM = 2x + 9 \)
Since point \( N \) is the midpoint of diagonal \( KM \), we have:
\[ KN = \frac{KM}{2} = \frac{5x + 1}{2} \] and \[ NM = 2x + 9. \]
Since \( KN \) is equal in length to \( NM \):
\[ \frac{5x + 1}{2} = 2x + 9. \]
To eliminate the fraction, we can multiply both sides by 2:
\[ 5x + 1 = 4x + 18. \]
Next, we will isolate \( x \) by subtracting \( 4x \) from both sides:
\[ 5x - 4x + 1 = 18, \] which simplifies to:
\[ x + 1 = 18. \]
Now, subtract 1 from both sides:
\[ x = 17. \]
So, the value of \( x \) is \( \boxed{17} \).