Answer:
x^2 - (4+13i)^2
Explanation:
This product has the form (a-b)(a+b), which is a 'special product' equal to a^2 - b^2. Following this pattern, [x-(4+13i)][x-(4+13i)] = x^2 - (4+13i)^2. The 2nd term could be expanded if desired, but the above result is the most compact one possible.