This answer is 18y • (y - 1)
Step by step solution:
Equation at the end of step 1:
[tex]9 (x - y) ^2 - 9 (x^{2} - y^{2})[/tex]
Equation at the end of step 2:
[tex]9 (x^2 + y^2 - 2xy) - 9 (x^2 - y^2)[/tex]
Equation at the end of step 3:
[tex]9x^2 + 9y^2 - 18xy - 9x^2 + 9y^2[/tex]
Equation at the end of step 4:
After performing basic +, - operation we get:
[tex]18y^2 - 18xy[/tex]
Answer is: 18y. (y – x)