Question 852878
{{{(-y-3x)(-y+3x)}}}



{{{-y(-y+3x)-3x(-y+3x)}}} Use the idea that {{{(a+b)(c+d)=a(c+d)+b(c+d)}}}



{{{-y(-y)-y(3x)-3x(-y)-3x(3x)}}} Distribute



{{{y^2-3xy+3xy-9x^2}}}



{{{y^2+0xy-9x^2}}}



{{{y^2+0-9x^2}}}



{{{y^2-9x^2}}}



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So {{{(-y-3x)(-y+3x)}}} expands and simplifies to {{{y^2-9x^2}}}