a) A−B−C=(5x3y−4xy2−6x2y2)−(−8xy3+xy2−4x2y2)−(x3+4x3y−6xy3−4xy2+5x2y2)
=5x3y−4xy2−6x2y2+8xy3−xy2+4x2y2−x3−4x3y+6xy3+4xy2−5x2y2
=x3y−xy2−7x2y2+14xy3−x3
b) B+A−C=(−8xy3+xy2−4x2y2)+(5x3y−4xy2−6x2y2)−(x3+4x3y−6xy3−4xy2+5x2y2)
=−8xy3+xy2−4x2y2+5x3y−4xy2−6x2y2−x3−4x3y+6xy3+4xy2−5x2y2
=−2xy3+xy2−15x2y2+x3y−x3
c) C−A−B=(x3+4x3y−6xy3−4xy2+5x2y2)−(5x3y−4xy2−6x2y2)−(−8xy3+xy2−4x2y2)
=x3+4x3y−6xy3−4xy2+5x2y2−5x3y+4xy2+6x2y2+8xy3−xy2+4x2y2
=x3−x3y+2xy3−xy2+15x2y2
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