(5.2x²y-3.4xy+8x³)+2(2.2xy-4x³-2.3x²y)其中x=-1/2,y=5
问题描述：
(5.2x²y-3.4xy+8x³)+2(2.2xy-4x³-2.3x²y)其中x=-1/2,y=5
答
(5.2x²y-3.4xy+8x³)+2(2.2xy-4x³-2.3x²y)
=5.2x²y-3.4xy+8x³+4.4xy-8x³-4.6x²y
=0.6x²y+xy
=xy（0.6x+1）
=-1/2*5（0.6*（-1/2）+1）=-5/2*7/10=-7/4
答
=0.6x²y+xy
=-7/4
答
(5.2x²y-3.4xy+8x³)+2(2.2xy-4x³-2.3x²y)
=5.2x²y-3.4xy+8x³+4.4xy-8x³-4.6x²y
=0.6x²y+xy
=0.6×(-1/2)²×5-1/2×5
=3/4-5/2
=-7/4