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JB
Lv 7
JB asked in Science & MathematicsMathematics · 6 years ago

What are the exact coordinates of the point of tangency?

The line y=mx is tangent to the curve y=2^x. What are the exact coordinates of the point of tangency?

2 Answers

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  • atsuo
    Lv 6
    6 years ago
    Favorite Answer

    Assume that the xy-coordinates of the point is (p,q) . Of course , q=2^p .

    (d/dx)2^x = (ln2)2^x , and you said the tangent is the line y =mx , so

    q = mp

    2^p = ((ln2)2^p)p

    1 = (ln2)p

    p = 1 / ln2

    q = 2^p = 2^(1 / ln2)

    ln(q) = ln(2^(1 / ln2))

    ....... = (1 / ln2)ln2

    ....... = 1

    So q = e ---> the xy-coordinates are (1 / ln2 , e)

  • y = mx has a slope of m

    y = 2^x

    y' = (2^x) * ln(2)

    m = ln(2) * 2^(x)

    m/ln(2) = 2^x

    ln(m / ln(2)) = x * ln(2)

    x = (1/ln(2)) * ln(m / ln(2))

    y = mx

    y = (m/ln(2)) * ln(m / ln(2))

    ((1/ln(2)) * ln(m / ln(2)) , (m / ln(2)) * ln(m / ln(2)))

    There's your point.

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