Question 430983
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Hi
Add 
1*(8x^2-3y^2-5xy) +1*(-12x^2-6y^2+9xy)   |applying distributive Principle
 8x^2-3y^2-5xy -12x^2-6y^2+9xy           |combining Like terms
   -4x^2-9y^2+4xy
or -(4x^2-4xy+ 9y^2)