You can put this solution on YOUR website! Find the solution of the equation on the interval [0,2pi]
sin 2(theta) + sin (theta) = 0
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sin2x+sinx=0
2sinxcosx+sinx=0
sinx(2cosx+1)=0
sinx=0
x=0
..
2cosx+1=0
2cosx=-1
cosx=-1/2
x=2π/3 and 4π/3 (quadrants II and III)
ans
theta=0, 2π/3 and 4π/3