已知x+y=1/5,xy=-1/2.求代数式(x+3y-3xy)-2(xy-2x-y)的值.
问题描述:
已知x+y=
,xy=-1 5
.求代数式(x+3y-3xy)-2(xy-2x-y)的值. 1 2
答
∵x+y=
,xy=-1 5
,1 2
∴(x+3y-3xy)-2(xy-2x-y)
=x+3y-3xy-2xy+4x+2y
=5x+5y-5xy
=5(x+y)-5xy
=5×
-5×(-1 5
)1 2
=3.5.