She's WRONG, so IGNORE her answer! You asked for sin (4θ) sin (2θ), but didn't get that. 

Answer by ikleyn(52803)   (Show Source): You can put this solution on YOUR website!
 .


The product to sum formula, relevant to this case, is


    .



In the formula, use  a= 4theta,  b= 2theta.   You will get


     = ,

or

     = .


It is your ANSWER




Solved, answered, explained and completed.







 

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