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Nilanjan Bhowmick AIR 3, CSIR NET (Earth Science)
Ujjawal vishal
i think u should post the pic including its preceding steps ...remember D^2 is replaced by -a^2 not by (-a)^2..If there is Cosx then a =1 so D^2 will be replaced by -(1^2) =-1..then the next step 3D+1 will be correct... Please do this type of questions carefully