Answer:
81
Step-by-step explanation:
The square of any binomial (ax + b) takes the form a²x² + 2abx + b²
We know a² = 1, meaning a = 1, and that 2ab = 18. So solve for b:
2 * 1 * b = 18
b = 9
Therefore the missing constant term is b² = 9² = 81
