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# Differentiation questions? C1 watch

1. Hi,

Please could I have some help on this question.

Q1. a) The tangent drawn to the curve at the point P (x, y) is parallel to the x-axis.
Determine the coordinates of P.

b) The line is a tangent to the curve at the point P (x, y). What are the coordinates of P?

I did the questions before that asked me to find the gradient/equation of the tangent and normal to curve, but don't understand this question, particularly the bit about coordinates and parallel to x-axis?

Thanks.
2. Q1. a) parallel to the x achsis means that the gradient is 0 ... so differentiate it and solve for x

b) you are given the equation of the line... y=mx+b where m is the gradient... if you differentiate the curve and let it equal to the gradient you can find then the x coordinate of P with that coordinate you can easily find the Y coordinate by simply plugging it into one of those equations
3. (Original post by darkness9999)
Q1. a) parallel to the x achsis means that the gradient is 0 ... so differentiate it and solve for x

b) you are given the equation of the line... y=mx+b where m is the gradient... if you differentiate the curve and let it equal to the gradient you can find then the x coordinate of P with that coordinate you can easily find the Y coordinate by simply plugging it into one of those equations
Thanks for the quick reply. On a I got x as - 3/4 which is right according to the book, and I thought

but according to the book it is , and therefore y = -9/8 . I don't understand why the is ignored..

Thanks
4. (Original post by Darkest Knight)
Thanks for the quick reply. On a I got x as - 3/4 which is right according to the book, and I thought

but according to the book it is , and therefore y = -9/8 . I don't understand why the is ignored..

Thanks

ok... in this question u already calculated the x value..which is right... then to get the Y value u just put the x value in the function... so y=2x^2 + 3x.... if u substitude x in there u will get - 9/8

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Updated: November 13, 2008
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