Answer:
xy = - 27
Step-by-step explanation:
Note that
(x - y)² = x² - 2xy + y² ← substitute given values, that is
9² = 27 - 2xy
81 = 27 - 2xy ( subtract 27 from both sides )
54 = - 2xy (divide both sides by - 2 )
- 27 = xy
