=3y²-x²-x²-3y²+2x-y=-2x²+2x-y=-18-6-2=-26
=ab-3a²-2b²-5ab-a²+2ab=-4a²-2b²-2ab=-4-8+4=-8这个已经是过程啦3y²-x²+（2x-y）-（x²+3y²）=3y²-x²-x²-3y²+2x-y=-2x²+2x-y=-18-6-2=-26 （ab-3a²）-2b²-5ab-（a²-2ab）=ab-3a²-2b²-5ab-a²+2ab=-4a²-2b²-2ab=-4-8+4=-8 已经很详细了