Hello!
The answer is:
[tex]-2x^{2}+3xy+8y^{2}[/tex]
Why?
When we have additions or differences of polynomials, we need to group each similar term, so:
[tex](-x^{2}+9xy)-(x^{2}+6xy-8y^{2})=-x^{2}+9xy-x^{2}-6xy+8y^{2}\\\\x^{2}+9xy-x^{2}-6xy+8y^{2}=-2x^{2}+3xy+8y^{2}[/tex]
So, the final polynomial is:
[tex]-2x^{2}+3xy+8y^{2}[/tex]
Have a nice day!
