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    can I have tan x in terms of tan 2x ?
    If yes
    write it
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    (Original post by zyiad)
    can I have tan x in terms of tan 2x ?
    If yes
    write it
    Take the identity for tan(2x) in terms of tan(x), reareange it into a quadratic for tan(x), solve it.
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    T = 2t/{ 1- t2 }

    make t the subject


    *T = tan2x

    t = tanx
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    (Original post by RDKGames)
    Take the identity for tan(2x) in terms of tan(x), reareange it into a quadratic for tan(x), solve it.

    I could not
    can you do it for me plz
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    (Original post by the bear)
    T = 2t/{ 1- t2 }

    make t the subject


    *T = tan2x

    t = tanx
    how?
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    (Original post by zyiad)
    how?
    rearrange it to get a quadratic equation with t as the variable, as RDK suggested above.
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    (Original post by zyiad)
    how?
    (Original post by the bear)
    rearrange it to get a quadratic equation with t as the variable, as RDK suggested above.

    I could not rearrange themcan you help me?
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    (Original post by zyiad)
    I could not rearrange themcan you help me?

    T = 2t/{ 1- t2 }

    T{ 1 - t2 } = 2t

    T - t2T = 2t

    - t2T = 2t - T

    t2T =- 2t +T

    t2T + 2t - T =0

    now use the quadratic formula with a = T, b = 2, c = -T
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    (Original post by the bear)
    T = 2t/{ 1- t2 }

    T{ 1 - t2 } = 2t

    T - t2T = 2t

    - t2T = 2t - T

    t2T =- 2t +T

    t2T + 2t - T =0

    now use the quadratic formula with a = T, b = 2, c = -T
    Thank you
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    (Original post by the bear)
    T = 2t/{ 1- t2 }

    T{ 1 - t2 } = 2t

    T - t2T = 2t

    - t2T = 2t - T

    t2T =- 2t +T

    t2T + 2t - T =0

    now use the quadratic formula with a = T, b = 2, c = -T
    There are two solutions to the equation.
    Can I exclude one of the solutions?
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    (Original post by zyiad)
    There are two solutions to the equation.
    Can I exclude one of the solutions?
    yes... for instance if T = tan 60°

    tan 30° = t

    ===> tan230° + 2tan30° - tan60° = 0

    this must only give a single, positive, value for tan30° so we can discard the negative answer.
 
 
 
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