The number of solutions of sinx+sin2x+sin3x=cosx+cos2x+cos3x,0≤x≤2π,is
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a
7
b
5
c
4
d
6
answer is D.
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Detailed Solution
We have (sinx+sin3x)+sin2x=(cosx+cos3x)+cos2x or 2sin2xcosx+sin2x=2cos2xcosx+cos2x or sin2x(2cosx+1)=cos2x(2cosx+1) or (2cosx+1)(sin2x−cos2x)=0 or cosx=−1/2 or sin2x−cos2x=0⇒ x=2nπ±(2π/3) or tan2x=1=tan(π/4)⇒ x=2nπ±(2π/3) or x=(4n+1)π/8,n∈ZBut here 0≤x≤2π. Hence, x=π/8,5π/8,2π/3,9π/8,4π/3,13π/8