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    Find the equation of the tangent to the curve at the point with he given x-coordiante.

    y=x^2 where x=-1

    I can find the equations normally when im given a pair of coordinates but here i only know x is -1 so im not sure what to do any help?
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    (Original post by hazbaz)
    Find the equation of the tangent to the curve at the point with he given x-coordiante.

    y=x^2 where x=-1

    I can find the equations normally when im given a pair of coordinates but here i only know x is -1 so im not sure what to do any help?
    What is y when x is -1?
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    well y = x^2 so...
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    Ah right ye my bad so Y is equal to 1
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    (Original post by hazbaz)
    Find the equation of the tangent to the curve at the point with he given x-coordiante.

    y=x^2 where x=-1

    I can find the equations normally when im given a pair of coordinates but here i only know x is -1 so im not sure what to do any help?
    When x=-1, y=1 by plugging it into y=x^2.
    Now differentiate to find the gradient at that point. Then express your line in whatever form you are used to i.e. y=mx+c or (y-y1)=m(x-x1) and substitute x1 and y1 as the x and y-values from above because the tangent must pass through that point.
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    (Original post by Farhan.Hanif93)
    When x=-1, y=1 by plugging it into y=x^2.
    Now differentiate to find the gradient at that point. Then express your line in whatever form you are used to i.e. y=mx+c or (y-y1)=m(x-x1) and substitute x1 and y1 as the x and y-values from above because the tangent must pass through that point.

    Ye so i have the point (-1,1)

    and diffrentiate to get y=2x

    at the point (-1,1) x = -1

    I worked out the gradient of the tangent to be -2

    So using Y=Mx+C Y=-2x+C

    at the point (-1,1) 1= -1 +C so i got C =2 therefore the equation is

    Y= -2x+2 but the book says the asnwer is Y=-2x -1 where have i gone wrong?


    I worked it out i didnt use teh tangent gradient in the Y=Mx+C
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    (Original post by hazbaz)
    So using Y=Mx+C Y=-2x+C

    at the point (-1,1) 1= -1 +C so i got C =2 therefore the equation is

    Y= -2x+2 but the book says the asnwer is Y=-2x -1 where have i gone wrong?
    The bit that I've highlighted in red is wrong... note that y=-2x+C and not y=x+C.

    EDIT: Oh you noticed. Never mind.
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    (Original post by hazbaz)
    Ye so i have the point (-1,1)

    and diffrentiate to get y=2x

    at the point (-1,1) x = -1

    I worked out the gradient of the tangent to be -2

    So using Y=Mx+C Y=-2x+C

    at the point (-1,1) 1= -1 +C so i got C =2 therefore the equation is

    Y= -2x+2 but the book says the asnwer is Y=-2x -1 where have i gone wrong?


    I worked it out i didnt use teh tangent gradient in the Y=Mx+C
    At the point (-1,1), x=-1 and y=1 so you need to plug those values into y=-2x+c so you get 1=2 + c, what is c?
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    (Original post by nuodai)
    The bit that I've highlighted in red is wrong... note that y=-2x+C and not y=x+C.

    EDIT: Oh you noticed. Never mind.
    Yep thanks for helping though
 
 
 
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