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    The point Q lies on C and is such that the gradient of the normal to C at Q is 1/7.

    Find the x coordinate of Q.

    The curve C has the equation of y = x^2 -9x +13

    --------------------------------

    The coordinates for y=f(x) are

    (-2, 0)
    ( 2,-3)
    ( 6, 0)

    How can I draw y = -2f(x)
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    (Original post by Tempa)
    The point Q lies on C and is such that the gradient of the normal to C at Q is 1/7.

    Find the x coordinate of Q.

    The curve C has the equation of y = x^2 -9x +13
    If the gradient of the normal is 1/7 then what is the gradient of the tangent at Q?

    Differentiate the function, make it = to the gradient above and solve for x
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    For 1 I got the x co-ord to be 1 , is that the answer ? . If it is i'll try go through it.

    For 2, because it's -2, its a stretch for each by -2 in the Y direction. So multiply the Y co-ord by -2 .

    (-2, 0) stays -2 , 0
    ( 2,-3) goes 2 , 6
    ( 6, 0) stays 6, 0
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    (Original post by gdunne42)
    If the gradient of the normal is 1/7 then what is the gradient of the tangent at Q?

    Differentiate the function, make it = to the gradient above and solve for x
    The gradient of the tangent is 3 as dy/dx is 2x - 9

    And the tangent is at point p to Curve C, at ( 6, -5)
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    (Original post by Tempa)
    The gradient of the tangent is 3 as dy/dx is 2x - 9

    And the tangent is at point p to Curve C, at ( 6, -5)
    Do you understand what a normal is?
    The normal at Q is perpendicular to the tangent at Q
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    (Original post by gdunne42)
    Do you understand what a normal is?
    The normal at Q is perpendicular to the tangent at Q
    No sir I do not know.
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    (Original post by Tempa)
    No sir I do not know.
    You should know from coordinate geometry that if 2 lines are perpendicular then the product of their gradient = -1
    or expressed another wayif m1 and m2 are the gradients of the 2 lines then m1 x m2 = -1

    So if the gradient of the normal at Q is 1/7 the gradient of the tangent must be -7 (1/7 x -7 = -1)

    Then 2x - 9 = -7

    Does this make any sense, because if not then it's seems premature to be trying exam questions.
 
 
 
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