#1
The straight line y=2x + c is a tangent to the curve =x^2 + 6x + 7.

A) Determine the value of the constant c.

should know it, but cant think of how o do it atm :[
#5
well thats what Im thinking but it doesnt quite seem to fit in my mind, dont know why.

on second thoughts it does work, It just eludes me exactly why.
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Last edited by dnjoe at Jan 14, 2007,
#6
once you've differentiated it, you find what x equals when y is 0 I think. I should know this too... I outta revise maths more

Then sub that into the original equation and thats it...i think
#8
No when you differntiate the curve you get the gradient function of the curve. Because it is 2x the gradient of the tanget is 2. Therefore 2=2x+6, 2x=-4, x=-2. Sub x=-2 into y=2x+c and solve it for c when y=0.
#10
Quote by shmooty
once you've differentiated it, you find what x equals when y is 0 I think. I should know this too... I outta revise maths more

Then sub that into the original equation and thats it...i think


no that would give you the gradient when y=0......aswell as the fact that we're dealing with the y-intercept(x=0) as opposed to the x-intercept(y=0).

I get it to be that when the tangent touches the curve they both have th same gradient so dy/dx = 2.

so 2x + 6 = 2

x = -2

when x = -2 y = -1

y = 2x + c

-1 = -4 + c

c = 3

doesnt seem right though.
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Well I can top you all, I've done my mum, my step brother AND a cat. As well as quite a few corpses.
#12
well its calculus, no idea when you guys start that in the US. Not particularly complicated stuff though.
songs: Left Behind choices
Quote by MadClownDisease
Well I can top you all, I've done my mum, my step brother AND a cat. As well as quite a few corpses.