1/x(x+3)+1/(x+3)(x+6)+1/(x+6)(x+9)=3/2(x+9)
(1/3)×[3/x(x+3)+3/(x+3)(x+6)+3/(x+6)(x+9)]=3/2(x+9)
(1/3)[(1/x-1/(x+3)+1/(x+3)-1/(x+6)+1/(x+6)-1/(x+9)]=3/2(x+9)
(1/3)[1/x-1/(x+9)]=3/2(x+9)
1/3x=3/2(x+9)+1/3(x+9)
1/3x=11/6(x+9)
x=2.
解题方法:裂项法.
1/x(x+3)+1/(x+3)(x+6)+1/(x+6)(x+9)=3/2(x+9)
(1/3)×[3/x(x+3)+3/(x+3)(x+6)+3/(x+6)(x+9)]=3/2(x+9)
(1/3)[(1/x-1/(x+3)+1/(x+3)-1/(x+6)+1/(x+6)-1/(x+9)]=3/2(x+9)
(1/3)[1/x-1/(x+9)]=3/2(x+9)
1/3x=3/2(x+9)+1/3(x+9)
1/3x=11/6(x+9)
x=2.
解题方法:裂项法.