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johnnyalln Group Title

Solve by factoring: 2sinxcosx=sinx in [0,2π)

  • 2 years ago
  • 2 years ago

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  1. ganeshie8 Group Title
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    begin by subtractcting sinx both sides, and then factor sinx

    • 2 years ago
  2. ganeshie8 Group Title
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    \(2\sin x \cos x=\sin x \) subtract sinx both sides \(2 \sin x \cos x - \sin x = 0\) factor out sinx \(\sin x (2 \cos x - 1) = 0 \)

    • 2 years ago
  3. ganeshie8 Group Title
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    We now have two factors whose product is zero, so the original equation will be satisfied when either factor is zero.

    • 2 years ago
  4. ganeshie8 Group Title
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    first set first factor = 0 => \(\sin x = 0\) the sin function 0, when \(x = 0 \) or \(x = \pi\) or \(x = 2\pi\)

    • 2 years ago
  5. ganeshie8 Group Title
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    similarly set the second factor = 0, and try getting other remaining solutions.

    • 2 years ago
  6. johnnyalln Group Title
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    I think i get this.. so the final answer would be x=0 or x=pi

    • 2 years ago
  7. ganeshie8 Group Title
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    not exactly thats half of the solutions only.. you need to set the second factor also equal to 0, and see what solutions u get

    • 2 years ago
  8. ganeshie8 Group Title
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    set second factor = 0 => \(2 \cos x -1 = 0\) \(\cos x = 1/2\) since, cos is positive in first and fourth quadrants : solution in first quadrant : \(x = \pi/3\) solution in fourth quadrant : \(x = 2\pi - \pi/3 = 5\pi/3\)

    • 2 years ago
  9. ganeshie8 Group Title
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    so, the solutions in interval \([0, 2\pi]\) are : \(0, \ \pi, \ \pi/3, \ 5\pi/3, \ 2\pi\)

    • 2 years ago
  10. johnnyalln Group Title
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    Got ya! I just got all of those except for 2pi..

    • 2 years ago
  11. johnnyalln Group Title
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    But yes makes perfect sense!

    • 2 years ago
  12. johnnyalln Group Title
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    Thanks a lot!

    • 2 years ago
  13. ganeshie8 Group Title
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    |dw:1352555743690:dw|

    • 2 years ago
  14. ganeshie8 Group Title
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    since we are looking for \(\sin x = 0\), we look at the graph of \(\sin\), see that the graph of \(\sin\) is becoming \(0\) when \(x = 0\) or \(x = \pi\) or \(x = 2\pi\) since all these 3 values of x are in the range \([0, 2\pi]\) , all 3 values satisfy the equation, and interval.

    • 2 years ago
  15. ganeshie8 Group Title
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    yw :)

    • 2 years ago
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