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# small exam question? Watch

1. Hello, I'm working through some past papers for c1 and I understand the first part of the question but I am struggling to see how "y=-15" for the second part, I would be extremely grateful for any help on this, thank you in advanced!

For part a: I know that dy/dx is " 1+24x^-2"

but for part B I know that to find the equation of the tangeant at C, it's y-y1=m(x-x1)

The question gives you "x=2" but I just don't understand on how to get "y1=-15"

The equation should be y-y1=7(x-2) but I need to work out y1 before I can carry out the equation!

2. (Original post by d_aan)

The question gives you "x=2" but I just don't understand on how to get "y1=-15"
You're looking for the tangent to the curve at the point (2, y). You have an equation for y, and a value for x.

Sub in x = 2 to your original equation.
3. When x=2, y =...?
4. Can't you sub the original x value into the y=equation ?
5. Thank you for the feedback everybody! Sorry, looking back at it now, that was such a simple step I should have carried out but my brain went dead and skipped it. Cheers for the help people, thread closed.

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Updated: December 29, 2010
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