Question

这三道数学题怎么做

1. -1x1/2= -1+1/2 -1/2X1/3= -1/2+1/3 - 1/3X1/4= -1/3+1/4 你发现的规律是? 用规律计算:(-1x1/2)+(-1/2X1/3)+(-1/3X1/4)+...+(-1/2004X1/2005)=? 已知a b 互为相反数，c d 互为倒数， x的绝对值等于2，试求 x²-(a+b+cd)乘于x+(a+b)两千零三次方+(-cd)两千零五次方

Answer 1

(1)(-1x1/2)+(-1/2X1/3)+(-1/3X1/4)+...+(-1/2004X1/2005)
=-1+1/2-1/2+1/3-……-1/2003+1/2004-1/2004+1/2005
=-1+1/2005
=-2004/2005
(2)a
b
互为相反数，得a+b=0
c
d
互为倒数，得cd=1
x的绝对值等于2，得x=正负2，x^2=4
x²-(a+b+cd)=3
x+(a+b)=正负2
(-cd)=-1
3*(正负2)^2003+(-1)^2005=3*(正负2)^2003-1
……