(1/2+1/3+...1/2009)(1+1/2+1/3+...1/2008)-(1+1/2+1/2009)(1/2+1/3+...+1/2008)答案等于多少?

来源:学生作业帮助网 编辑:作业帮 时间:2024/05/09 22:47:51
(1/2+1/3+...1/2009)(1+1/2+1/3+...1/2008)-(1+1/2+1/2009)(1/2+1/3+...+1/2008)答案等于多少?

(1/2+1/3+...1/2009)(1+1/2+1/3+...1/2008)-(1+1/2+1/2009)(1/2+1/3+...+1/2008)答案等于多少?
(1/2+1/3+...1/2009)(1+1/2+1/3+...1/2008)-(1+1/2+1/2009)(1/2+1/3+...+1/2008)答案等于多少?

(1/2+1/3+...1/2009)(1+1/2+1/3+...1/2008)-(1+1/2+1/2009)(1/2+1/3+...+1/2008)答案等于多少?
令a=1/2+1/3+...+1/2008
则原式=(a+1/2009)(1+a)-(1+a+1/2009)a
=a(1+a)+1/2009(1+a)-a(1-a)-1/2009a
=1/2009(1+a)-1/2009a
=1/2009+1/2009a-1/2009a
=1/2009

1/2+1/3+...+1/2008=t
原式=(t+1/2009)(1+t)-(1+t+1/2009)(t)
=1/2009

令A=1/2+1/3+...1/2009,令B=1/2+1/3+...+1/2008;
原式=A(1+B)-(1+A)B=A-B=1/2009