The no. of real solution of the equation sinx+2sin2x−sin3x=3, where x∈(0,π).
MyTry:: Given (sinx−sin3x)+2sin2x=3
⇒−2cos2x⋅sinx+2sin2x=3⇒−2cos2x⋅sinx+4sinx⋅cosx=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(1−2sin2x)
Thus we get
0=sinx+4sinxcosx−2sinxcos2x−sinx+2sin3x
Divide al through by sinx (why can we?):
4cosx−2cos2x+2sin2x=0⟺2cosx−cos2x+1−cos2x=0⟺
2cos2x−2cosx−1=0⟺…
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