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Math Help - tangents

  1. #1
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    tangents

    i have two tangents that i have the equations to. the question asks to find the co-ordinates were the two tangents intersect. i am guessing that i will have use the two tangent equations in a similtaneous equation but i dont know how can some one help me ? the two equations are Y=5x-90 at x=5 and y=-16x-2024 at x=6
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  2. #2
    Super Member 11rdc11's Avatar
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    equal your equations to each

    5x - 90 = -16x -2024

    21x = -1934

    x = \frac{-1934}{21}

    so now just plug in x into one of your original equations and it will give you your y

    If you have any questions feel free to ask.
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  3. #3
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    im still having trouble with it im getting an y value of -550.47 this is far to great to be real on my graph i think the problem lies in thi equation y=-16x-2024
    my dy/dx was 3x^2-12x-31 ax was 6 could some one see if they got the same answer as me
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  4. #4
    Super Member 11rdc11's Avatar
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    What was the original function before you took the derivative and what was the original question you were working on?
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  5. #5
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    x^3-6x^2-31x+120 was the original function the question was to take a point one with a posotive gradient and one with a negative gradient on the cubic that i found from the equation x^3-6x^2-31x+120 and draw a tangent i then had to work out the tangent equation. i then had to extend the tangents until they intersect and find the co-ordinate at which they intersect
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