Another method

S=S(x)

Obiviously,the soltion must less than zero.

let x=-1, get 2a+b<2, and the area of the cross section between 2a+b<2 and 0
Let x=-2 and -2/1, get the same equation 10a+4b<17, then get S=0;

Observing the equation, we can have
f(x)<0 and f(1/x)<0
are the same.

S(x) has a characteristc, which is
S(x) is a non-increasing fuction in (-1,0) and
S(x) is a non-decreasing fuction in (-infinity,-1),
S(-1) is the maximum, and S(-1)=-1/4 is the solution.

所有跟帖： 

• 回复：Another method -yma16- ♂ (46 bytes) () 04/01/2008 postreply 20:11:01

• 回复：回复：Another method -sxcxm- ♂ (747 bytes) () 04/02/2008 postreply 17:22:05

• 回复：回复：回复：Another method -yma16- ♂ (291 bytes) () 04/03/2008 postreply 09:02:18

• 回复：回复：Another method(Picture) (图) -sxcxm- ♂ (68 bytes) () 04/02/2008 postreply 17:33:10

• This is also a great solution.... -乱弹- ♂ (80 bytes) () 04/02/2008 postreply 20:33:22

• 回复：回复：Another method (图) -sxcxm- ♂ (79 bytes) () 04/04/2008 postreply 14:46:07

• My idea is (图) -sxcxm- ♂ (68 bytes) () 04/04/2008 postreply 14:48:15