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Finding the equation of a parabola? (Calculus)?

Find an equation of the parabola y = ax^2 + bx + c that passes through (0,1) and is tangent to the line y = x - 1 at (1,0)

I don't even know where to start :(...we didnt even do this in class

1 Answer

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  • DWRead
    Lv 7
    10 years ago

    y = ax² + bx + c passes through (0, 1) and (1, 0).

    1 = a·0² + b·0 + c

    c = 1

    0 = a·1² + b·1 + 1

    a = -b - 1

    Parabola and line have same slope at the point of tangency.

    slope of line = 1

    slope of parabola = y' = 2ax + b

    point of tangency: (1, 0)

    2a·1 + b = 1

    2(-b - 1) + b = 1

    -b = 3

    b = -3

    a = 2

    y = 2x² - 3x + 1

    http://www.flickr.com/photos/dwread/6205275696/

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