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    3 cos x + cot x = 0

    What do I do now?

    3 cos x + 1/tan x = 0

    Then what?

    Please help.

    Thank you

    Jorge
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    (Original post by Jorge)
    3 cos x + cot x = 0
    3cosx + cosx/sinx = 0
    3cosxsinx + cosx = 0
    cosx[3sinx + 1] = 0
    cosx = 0 or sinx=-1/3
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    jesus christ lad!

    3cosxsinx + cosx = 0

    thats is cosx(3sinx+1) = 0

    DONT FORGET THE cosx=0 else you lose solutions!
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    (Original post by Jorge)
    3 cos x + cot x = 0

    What do I do now?

    3 cos x + 1/tan x = 0

    Then what?

    Please help.

    Thank you

    Jorge
    Change to 3cosx + cosx/sinx = 0
    get the whole LHS over sin x
    get to cosx(3 sinx + 1)/sin x = 0

    be careful not to "lose" solutions if you cancel.

    Aitch
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    Mm, thanks for the correction.
    I haven't done much pure based work since September. Just M2/M3/D1 mainly.
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    seems to be some consensus here then!

    Aitch
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    Brilliant

    Would you like to do the exam for me?

    How about:

    sqrt3 cot x + 1 = 0


    Thanks

    Jorge
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    Sorry forget it. I got it

    sqrt3/tanx = -1

    sqrt3 = -tan x

    tanx = -sqrt3

    x = 120 or 300

    Thanks

    Jorge
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    (Original post by Jorge)
    Brilliant

    Would you like to do the exam for me?

    How about:

    sqrt3 cot x + 1 = 0


    Thanks

    Jorge
    -sqrt3=tanx
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    Another one?

    sec(2x - 60) = - 2/sqrt3

    1/cos(2x - 60) = - 2/sqrt3

    -2 cos(2x - 60) = sqrt3

    cos(2x - 60) = - sqrt3/2

    (2x - 60) = 150

    2x = 210

    x = 105

    Solutions 105 and (360-105) 255

    But the book's solutions are

    105, 135, 285, 315

    What have I done wrong?

    Thanks

    Jorge
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    because you have worked out 2x u need to change the limits.
    If 0 < x < 360 then for 0 < 2x < 720.
    Then u will get 4 answers not 2.
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    Got it, thanks

    Jorge
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    One more please, before lunch:

    2 tan x = cot x + 1

    2 tan x = 1/tan x + 1

    2 tan^2 x = 2

    tan^2 x = 1

    tan x = +/- 1

    x = 45 or -45

    Angles 45, 135, 225, 315

    But the book says: 45, 153.4, 225, 333.4

    What did I do wrong?

    Thanks
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    2tanx = cotx + 1
    2tanx = 1/tanx + 1
    2tanx^2 = 1 + tanx
    2tanx^2 - tanx - 1 = 0

    let tanx = y

    2y^2 - y - 1 = 0
    (2y+1) (y-1) = 0
    y = -1/2 or y=1

    therefore:

    tanx = -1/2 or tanx = 1
    x= -26.6 x = 45 and (180+45=) 225
    = (180+(-26.6))
    = 153.4
    and (360-26.6=) 333.4
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    post your questions HERE :mad: :mad:
 
 
 
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