若xy=-2,x+y=3,求代数式（3xy+10y)+{5x-(2xy+2y-3x)}的值

题目

若xy=-2,x+y=3,求代数式（3xy+10y)+{5x-(2xy+2y-3x)}的值

答案

（3xy+10y)+{5x-(2xy+2y-3x)}
=3xy+10y+5x-2xy-2y+3x
=xy+8x+8y
=xy+8(x+y)
xy=-2 x+y=3
xy+8(x+y)
=-2+8×3
=22