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    • Thread Starter
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    How to do you solve

    2sinxcosx = - sinx

    In the range 0degrees </= x </= 360 degrees?
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    Sin x is on both sides so that can be removed by dividing.
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    (Original post by Phoebus Apollo)
    How to do you solve

    2sinxcosx = - sinx

    In the range 0degrees </= x </= 360 degrees?
    Rearrange to get = 0 and factorise. Once it's factorised think about how you would solve a factorised quadratic.
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    (Original post by Vikingninja)
    Sin x is on both sides so that can be removed by dividing.
    Dividing results in loss of solutions. Always factorise.

    What have you tried, OP?
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    (Original post by Phoebus Apollo)
    How to do you solve

    2sinxcosx = - sinx

    In the range 0degrees </= x </= 360 degrees?
    You need to get all x terms on one side so the other side =0, and then factorise to solve, setting each factor which can =0 to 0. If this is confusing, tell me.
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    (Original post by Vikingninja)
    Sin x is on both sides so that can be removed by dividing.
    Doing so will lose a root. You can only divide both sides of an equation by something if you know that something is non-zero.
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    (Original post by Vikingninja)
    Sin x is on both sides so that can be removed by dividing.
    You lose a solution if you divide by sinx

    Damn, I got beaten
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    Roughly like this
    2sinxcosx + sinx = 0
    sinx(2cosx +1) = 0
    sinx= 0 and 2cosx+1=0

    then just solve as normal
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    (Original post by Vikingninja)
    Sin x is on both sides so that can be removed by dividing.
    But don't forget sinx = 0...
    I did that once, my C2 result still haunts me
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    (Original post by Vikingninja)
    Sin x is on both sides so that can be removed by dividing.
    I hope you're joking.
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    (Original post by SeanFM)
    Dividing results in loss of solutions. Always factorise.

    What have you tried, OP?
    I made up the question because I wanted to see whether i should divide or factorise in that situation. Thanks for your reply!
    By the way If you had:
    2sinx/cost = -1/cosx and you cross multiplied, what would you do then?
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    (Original post by Phoebus Apollo)
    I made up the question because I wanted to see whether i should divide or factorise in that situation. Thanks for your reply!
    By the way If you had:
    2sinx/cost = -1/cosx and you cross multiplied, what would you do then?
    Assuming that's cosx and not cost, I'd rearrange that to make it equal to 0 and see that it doesn't matter what cosx is as it is on the denominator.
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    (Original post by SeanFM)
    Assuming that's cosx and not cost, I'd rearrange that to make it equal to 0 and see that it doesn't matter what cosx is as it is on the denominator.
    So you would only get sinx = -1/2?
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    (Original post by Phoebus Apollo)
    So you would only get sinx = -1/2?
    Yes.
 
 
 
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