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    Hi,

    Please could I have some help on this question.

    Q1. a) The tangent drawn to the curve  y = 2x^2 + 3x at the point P (x, y) is parallel to the x-axis.
    Determine the coordinates of P.

    b) The line  y = 2x - 4 is a tangent to the curve  y = x^2 - 2x 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.
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    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
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    (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 y = 2  -\frac{3}{4}^2 + (3 x -\frac{3}{4})

    but according to the book it is y = 2  -\frac{3}{4}^2 , and therefore y = -9/8 . I don't understand why the + 3 x -\frac{3}{4} is ignored..

    Can you explain please?

    Thanks
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    (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 y = 2  -\frac{3}{4}^2 + (3 x -\frac{3}{4})

    but according to the book it is y = 2  -\frac{3}{4}^2 , and therefore y = -9/8 . I don't understand why the + 3 x -\frac{3}{4} is ignored..

    Can you explain please?

    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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