求值:x(x+2y)-(x+1)2+2x,其中x=1/25,y=−25.

问题描述:

求值:x(x+2y)-(x+1)2+2x,其中x=

1
25
,y=−25.

x(x+2y)-(x+1)2+2x
=x2+2xy-(x2+2x+1)+2x
=x2+2xy-x2-2x-1+2x
=2xy-1.
x=

1
25
,y=−25时,
原式=2xy-1,
=2×
1
25
×(-25)-1,
=-3.