( 3y - x )” - ( y + 3x )”
= ( x - 3y )” - ( 3x + y )”
= [ (x-3y) - (3x+y) ][ (x-3y) + (3x+y) ]
= ( x - 3y - 3x - y )( x - 3y + 3x + y )
= ( -2x - 4y )( 4x - 2y )
= -4( x + 2y )( 2x - y )
(3y-x)^2-(y+3x)^2=[(3y-x)-(y+3x)][(3y-x)+(y+3x)]
=(2y-3x)(4y+2x)
=2(2y-3x)(2y+x)
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