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Thread: Help on Parametrics!

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    Help on Parametrics!

    I am currently having trouble with part b - any help would be appreciated.

    7a) Find where the line y= 3x + 4 intersects the parabola 2y=5x^2
    Answers: (2,10) and (-4/5, 8/5)

    7b) Find the equations of the tangents to the parabola at the points of intersection.

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    Re: Help on Parametrics!

    Dont u just differentiate the equation of the parabola, find the gradients at x=2 and x=-4/5 and sub into y-y1=m(x-x1)? i start parametrics next term so maybe im wrong

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    Re: Help on Parametrics!

    Find the derivative of the parabola at each poiints and then use the point-gradient formula to find the eqn of tangents

    y = 5/2 x^2

    dy/dx = 5x

    at x = 2, dy/dx = 10
    therefore, the eqn of tangent at (2,10) is y - 10 = 10(x-2) [rearrange into the general form]

    at x = -4/5, dy/dx = -4
    therefore, the eqn of tangent at (-4/5, 8/5) is y - 8/5 = -4(x + 4/5) [again, rearrrange it]
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    Re: Help on Parametrics!

    Quote Originally Posted by jathu123 View Post
    Find the derivative of the parabola at each poiints and then use the point-gradient formula to find the eqn of tangents

    y = 5/2 x^2

    dy/dx = 5x

    at x = 2, dy/dx = 10
    therefore, the eqn of tangent at (2,10) is y - 10 = 10(x-2) [rearrange into the general form]

    at x = -4/5, dy/dx = -4
    therefore, the eqn of tangent at (-4/5, 8/5) is y - 8/5 = -4(x + 4/5) [again, rearrrange it]
    Thanks!

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