document.write( "Question 156521: Adapted from Algebra and Trigonometry by P. Forester but I have a textbook by Holt\r
\n" ); document.write( "\n" ); document.write( "Prove the product of two negatives is a positive\r
\n" ); document.write( "\n" ); document.write( "(-x)(-y) = (-1*x)(-1*y) Identity
\n" ); document.write( " = (-1)[x*(-1)](y) distributive
\n" ); document.write( " = (-1)[-1*x](y)
\n" ); document.write( " = [-1*(-1)] xy
\n" ); document.write( " = 1*xy
\n" ); document.write( " = xy
\n" ); document.write( "therefore (-x)(-y) = xy \n" ); document.write( "
Algebra.Com's Answer #115395 by stanbon(75887)\"\" \"About 
You can put this solution on YOUR website!
We know -(xy) + xy = 0 by definition of additive inverse
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\n" ); document.write( "Now show -(-xy) + xy = 0 where x and y are both positive numbers.
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\n" ); document.write( "(-x)(-y) = (-1)(x)(-y) -----associative law
\n" ); document.write( "(-1)[(x)(-y)]=(-1)(-xy)--associative law & (positive * negative is negative)
\n" ); document.write( "(-1)(-xy) + (-xy) = 0 definition of additive inverse
\n" ); document.write( "Therefore (-1)(-xy) = xy ... uniqueness of additive inverse
\n" ); document.write( "Therefore (-x)(-y) = xy ... argument above
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\n" ); document.write( "Cheers,
\n" ); document.write( "Stan H.
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