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# C3 Edexcel trig watch

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1. 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
2. Sin 4x = Sin (2x + 2x) = 2Sin 2x Cos 2x.

Then replace all the x's with k's and you've done it.
3. lol sorry, im still lost, I dont get how the Sin (2x+2x) comes from 2sin 2x Cos 2x
4. 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)

5. (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

6. (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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