Question

x^2-2x+1/x^2-1+x-1/x^2+x-x的值，其中x=2007,某同学把x=2007错抄成x=2008,但它的结果与正确答案相同，为

Answer 1

原式=(x-1)^2/(x+1)(x-1)+(x-1)/x(x+1)-x
=(x-1)/(x+1)+(x-1)/x(x+1)-x
=(x^2-x+x-1)/(x+1)-x
=(x+1)(x-1)/(x+1)-x
=x-1-x
=-1
所以不论x取何值，结果都是-1

Answer 2

2x+6y+8z=6 (1)
3x—12y+7z=—3 (2)
4x—3y+4z=11 (3)
(1)+(3)*2
10x+16z=28
5x+8z=14 (4)
(1)*2+(2)
7x+23z=9 (5)
(5)*5-(4)*7
115z-56z=45-98
59z=-53
z=-53/59
x=(9-23z)/7=250/59
y=(3x+7z+3)/12=139/177