Thursday, 27 July 2017

algebra precalculus - real solution of eqn. in sinx+2sin2xsin3x=3, where xin(0,pi).



The no. of real solution of the equation sinx+2sin2xsin3x=3, where x(0,π).




MyTry:: Given (sinxsin3x)+2sin2x=3



2cos2xsinx+2sin2x=32cos2xsinx+4sinxcosx=3



2sinx(cos2x+2cosx)=3



Now I did not understand how can i solve it.



Help me




Thanks


Answer



{sin2x=2sinxcosxsin3x=sin2xcosx+sinxcos2x=2sinxcos2x+sinx(12sin2x)



Thus we get



0=sinx+4sinxcosx2sinxcos2xsinx+2sin3x



Divide al through by sinx (why can we?):




4cosx2cos2x+2sin2x=02cosxcos2x+1cos2x=0



2cos2x2cosx1=0


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