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    Sinsquared X ≥ 1/4
    (0<x<360)

    can anyone solve this?^o)

    thought of doing : sinX ≥ √1/4
    but its wrong.
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    (sinx)^2 >= 1/4
    sinx >= 1/2
    If you draw y = sinx, the curve is above 1/2 between 30 and 150, so:
    30 <= x <= 150
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    sinx ≥ 1/2 and -1/2 ≥ sinx

    150 ≥ x ≥ 30 and 330 ≥ x ≥ 210
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    (Original post by Dez)
    (sinx)^2 >= 1/4
    sinx >= 1/2
    If you draw y = sinx, the curve is above 1/2 between 30 and 150, so:
    30 <= x <= 150
    youve forgotten the negative root of 1/4
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    Edit: Wow, beaten to the post by the world and his goat - carry on
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    Whoops, forgot the negative one :P

    Edit: And beaten to the realisation too
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    teacher stated that cannot simply take sqaureroot of 1/4 and therefore cannot do:
    sinX > +-1/2
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    Why not?
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    (Original post by shah)
    teacher stated that cannot simply take sqaureroot of 1/4 and therefore cannot do:
    sinX > +-1/2
    sin2(x) >= 1/4

    Using identity: ½(1-cos(2x) = sin2(x)

    -> ½(1-cos(2x) >= 1/4
    -> 1-cos(2x) >= ½
    -> cos(2x) >= ½
    -> x >= ½arccos(½)
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    duno why hoping someone here could answer that. lol
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    (Original post by shah)
    teacher stated that cannot simply take sqaureroot of 1/4 and therefore cannot do:
    sinX > +-1/2
    sin2(x) >= 1/4

    Using identity: ½(1-cos(2x)) = sin2(x)

    -> ½(1-cos(2x) >= 1/4
    -> 1-cos(2x) >= ½
    -> cos(2x) =< ½
    -> x =< ½arccos(½)
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    thnks for tht.
    is there an specific identity as : ½(1-cos(2x)) = sin2(x) ?
    or is that wrked out from sin^2x + cos^2x=1.
    b'cause this is a C2 Q.?
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    (Original post by shah)
    thnks for tht.
    is there an specific identity as : ½(1-cos(2x)) = sin2(x) ?
    or is that wrked out from sin^2x + cos^2x=1.
    b'cause this is a C2 Q.?
    If it's a C2 question then the 2nd post is correct. You just square root the RHS and take arcsin of that.
 
 
 

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