问题
解答题
先化简,再求值. (1)(3x+2)(3x-2)-5x(x-1)-(2x-1)2,其中x=-
(2)(
|
答案
(1)(3x+2)(3x-2)-5x(x-1)-(2x-1)2
=9x2-4-5x2+5x-4x2+4x-1
=9x-5,
当x=-
时,原式=9×(-1 3
)-5=-3-5=-8;1 3
(2)(
)•(x2y-4y3 x2+4xy+4y2
+x)4xy x-2y
=
•y(x+2y)(x-2y) (x+2y)2 x(x+2y) x-2y
=xy,
当x=
-1,y=2
+1时,原式=xy=(2
-1)×(2
+1)=2-1=1.2