dk; 1-4x^2>=0 va x khac 0 tuog duog voi
-1/2=<x=<1/2 va x khac 0
bpt tuog duog voi:
[(1-can(1-4x^2)] . [(1+can(1-4x^2)] / x . [1+can(1-4x^2)] < 3
<=> 4x^2/x.[1+can(1-4x^2)] < 3
<=> 4x<3[1+can(1-4x^2)] (do 1+ can(1-4x^2) >0)
<=> 4x-3<3can(1-4x^2)
den day cta chia thanh 2TH
+TH1;
do 3can(1-4x^2)>=0 nen chi can 4x-3<0 suy ra x<3/4
+TH2:
{4x-3>=0
{(4x-3)^2<9(1-4x^2)
<=> {x>=3/4
******{52x^2-24x<0
<=>
{ x>=3/4
{0<x<6/13
suy ra x>=3/4
vay bpt co nghiem tren R
