先化简,再求值：5x2-[2xy-3（xy+2）+4x2] ,其中x=-2,y= .先化简,再求值：5x2-[2xy-3（xy+2）+4x2] ,其中x=-2,y=1/2 .
问题描述：
先化简,再求值：5x2-[2xy-3（xy+2）+4x2] ,其中x=-2,y= .
先化简,再求值：5x2-[2xy-3（xy+2）+4x2] ,其中x=-2,y=1/2 .
答
5x2-[2xy-3（xy+2）+4x2]
=5x2-[2xy-3xy-6+4x2]
=5x2-2xy+3xy+6-4x2
=x2+xy+6
=9
答
5x2-[2xy-3（xy+2）+4x2]
=5x2-(2xy-3xy-6+4x2)
=5x2-2xy+3xy+6-4x2
=x2+xy+6
=(-2)^2-2*1/2+6
=9
答
首先去掉括号,化简
原式=5x2-2xy+3(xy+2)-4x2
=5x2-4x2-2xy+3xy+6
=x2+xy+6
=4-1+6
=9
答
=5x^2y-(8xy-6xy+9-x^2y)+1
=5x^2y-(2xy+9-x^2y)+1
=5x^2y-2xy-9+x^2y+1
=6x^2y-2xy-8
=-3+2-8
=-9