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=
,y=−25. 1 25
答
x(x+2y)-(x+1)2+2x
=x2+2xy-(x2+2x+1)+2x
=x2+2xy-x2-2x-1+2x
=2xy-1.
当x=
,y=−25时,1 25
原式=2xy-1,
=2×
×(-25)-1,1 25
=-3.