Q.

The equation  2(log3x)2|log3x|+a=0  has exactly four real solutions if  a(0,1K) , then the value of K is __

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answer is 8.

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Detailed Solution

on putting   log3x=t,  we get
  2t2|t|+a=0     …(i)
If  t>0,   then   2t2t+a=0   …(ii)
If  t<0,  then    2t2+t+a=0    …(iii)
If Eq. (i) has four roots then Eq. (ii) must have both roots positive and Eq. (iii) has both roots negative. Now, Eq. (ii) has both roots positive, if D > 0 
  a/2>0
   18a>0,a>0
a(0,18)   on taking intersection.
Again, Eq. (iii) has both roots negative, if  D>0,a/2>0.
We again get  a(0,18)K=8

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The equation  2(log3x)2−|log3x|+a=0  has exactly four real solutions if  a∈(0,1K) , then the value of K is __