You can put this solution on YOUR website! (6x^2-3xy+y^2)+(-9x[^2]-8xy-y^2)+(x^2+xy-8y^2)
I'll assume there should be a (^) after the -9x in the second term.
6x^2-3xy+y^2
-9x^2-8xy-y^2
x^2+xy-8y^2 now add.
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-2x^2-10xy-8y^2
-2(x^2+5xy+4y^2)
-2(x+4)(x+1) ans.