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C3 Edexcel trig watch

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    y = (2x – 1) tan 2x,

    The curve has a minimum at the point P. The x-coordinate of P is k.


    Show that k satisfies the equation
    4k + sin 4k – 2 = 0.

    I got up to:

    2sin2xCos2x + 4x - 2 = 0

    but unsure how I go further..

    thanks
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    Sin 4x = Sin (2x + 2x) = 2Sin 2x Cos 2x.

    Then replace all the x's with k's and you've done it.
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    lol sorry, im still lost, I dont get how the Sin (2x+2x) comes from 2sin 2x Cos 2x
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    2SinA Cos A = Sin 2A is your identity for Sin 2A. That identity works no matter what letter or number you use instead of A.
    2Sin M Cos M = Sin 2M
    2Sin(2x) Cos(2x) = Sin (4x)

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    (Original post by dietwater)
    lol sorry, im still lost, I dont get how the Sin (2x+2x) comes from 2sin 2x Cos 2x
    It's the double angle formula...

    sin(x + x) = sinxcosx + sinxcosx = 2sinxcosx

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    (Original post by grace_)
    2SinA Cos A = Sin 2A is your identity for Sin 2A. That identity works no matter what letter or number you use instead of A.
    2Sin M Cos M = Sin 2M
    2Sin(2x) Cos(2x) = Sin (4x)

    ah, thanks yeah the 2x confused me sorry lol
 
 
 
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