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    Given that f(x)=2x^2 +8x+3 and the line y=4x+c which is a tangent to the curve f(x).
    Calculate c.
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    (Original post by AverageJoe22)
    Given that f(x)=2x^2 +8x+3 and the line y=4x+c which is a tangent to the curve f(x).
    Calculate c.
    There will only be one point of intersection between a quadratic and its tangent. Use the discriminant?
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    find where y = 2x2 + 8x + 3 meets y = 4x + c

    you will end up with a quadratic equation. the discriminant has to be a certain value for there to be a single solution.
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    Make f'(x) = 4 as you know the gradient of the tangent is 4.
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    (Original post by the bear)
    find where y = 2x2 + 8x + 3 meets y = 4x + c

    you will end up with a quadratic equation. the discriminant has to be a certain value for there to be a single solution.
    what value?
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    (Original post by AverageJoe22)
    what value?
    so if D is positive you get 2 results

    if D is negative you get 0 results...

    i am not allowed to give complete answers
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    (Original post by the bear)
    so if D is positive you get 2 results

    if D is negative you get 0 results...

    i am not allowed to give complete answers
    i'll assume it has to equal 0in order to obtain 1 solution
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    (Original post by ubisoft)
    Make f'(x) = 4 as you know the gradient of the tangent is 4.
    By far the easiest method - can be done as mental arithmetic.

    c=1
 
 
 
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