已知x-y=3,xy=4,则代数式(3x-4y+5xy)-(2x-3y)+5xy的值是?

问题描述:

已知x-y=3,xy=4,则代数式(3x-4y+5xy)-(2x-3y)+5xy的值是?

(3x-4y+5xy)-(2x-3y)+5xy
=3x-4y+5xy-2x+3y+5xy
=(3-2)x-(4-3)y+(5+5)xy
=x-y+10xy
因:x-y=3,xy=4 代入上式可得:
原式=3+40=43

原式=3x-4y+5xy-2x+3y+5xy
=x-y+10xy
=3+10×4
=43

(3x-4y+5xy)-(2x-3y)+5xy
=3x-2x-4y+3y+5xy+5xy
=x-y+10xy
=3+4×10
=43