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# Easy C1 question I can't do! watch

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1. Heyy

I don't know what I am doing wrong, so could someone help me out?

a) find the equation of the tangent to the curve at the point with the given x co-ordinate.

y=x^2 where x= -1

now I know first you differentiate to get 2x, and then substitute -1 into 2x to get -2.

so then y-0=-2(x+1)
therefore y=-2x-2?

but the book said its y=-2x-1?? can someone please tell me where I have gone wrong

thanks, rep will be given
2. y= -1
3. That means the slope is -2. That part you did correct.
Second step is to find x and y at -1. So x = -1 and y = 1.

Third step is to plug it into the y=mx+b form. where m is the slope, -2.

1 = -2(-1) + b.
b = 1-2 = -1

So the final answer is y=-2x-1

--Daniel
4. (Original post by J DOT A)
Heyy

I don't know what I am doing wrong, so could someone help me out?

a) find the equation of the tangent to the curve at the point with the given x co-ordinate.

y=x^2 where x= -1

now I know first you differentiate to get 2x, and then substitute -1 into 2x to get -2.

so then y-0=-2(x+1)
therefore y=-2x-2?

but the book said its y=-2x-1?? can someone please tell me where I have gone wrong

thanks, rep will be given

there
It should be y-1=-2(x+1)
5. (Original post by logic123)
y= -1
no it isnt ..y=+1
6. yer im drunk to much vodka
7. if u use the equation y-y1=m(x-x1)

then you need to find y1 which is...

y1= x1^2
y1=(-1)^2
y1=+1

y-y1=m(x-x1)
y-1=-2(x-(-1))
y-1=-2(x+1)
y-1= -2x-2
y=-2x-1

usman(uah9) hope that helps

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Updated: October 11, 2009
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