Answer:
1.A+B=2y²+3x-x²+3x²-y²=y²+3x+2x²
2.A-B=2y²+3x-x²-3x²+y²=3y²+3x-4x²
3.B+C=3x²-y²+5x²-3xy=8x²-3xy-y²
4.B-C=3x²-y²-5x²+3xy=3xy-2x²-y²
5.A+B+C=2y²+3x-x²+3x²-y²+5x²-3xy
=y²+3x+2x²+5x²-3xy=y²+3x-3xy+7x²
6.A+B-C=y²+3x+2x²-5x²+3xy=y²+3x+3xy-3x²
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