kangfanger
幼苗
共回答了16个问题采纳率:81.3% 举报
1、化简=a-{b-2a+[3a-2b-4a+5b]}
=a-{4b-3a}
=4a-4b
代入a=2009,b=2010
结果=-4
2、x²+xy=2,y²+xy=5,可知
x²+2xy+y²=5+2=7
1/2x²+xy+1/2y²=1/2(x²+2xy+y²)=1/2×7=7/2
3、根据题目:3x=2,y=1,故x=2/3 ,y=1
3xy²-【2x²y-2(xy-3/2xy²)+xy】+3x²y
=3xy²-[2x²y-xy+3xy²]+3x²y
=x²y+xy
代入x=2/3 ,y=1
结果=10/9
1年前
3