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Datx
Lv 6
Datx asked in Science & MathematicsMathematics · 10 years ago

The tangent to the curve y = x−3x^(-1) at (x, y) = (1,−2) meets the x-axis at (a,0) where a =?

I have been trying to figure out what exactly this questions means. I can find the derivative of the y, it's 1+3/x^2. However, I don't get what this question is asking me to solve for.

Thanks.

2 Answers

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  • 10 years ago
    Favorite Answer

    y = x - 3x^(-1)

    dy/dx = 1 + 3/(x^2)

    Slope of tangent to curve at (1, - 2) = 1 + 3 = 4

    Eqn of tangent line:

    y + 2 = 4(x - 1)

    y = 4x - 6

    Find the x-intercept:

    4x - 6 = 0

    x = 3/2

    Therefore, a = 3/2

  • 10 years ago

    it means the line given by the tangent to the curve at (1,-2) intersects the x axis at a certain point (a,0)

    so basically you have to find the equation of a line where the slope (m) is equal to y' at x= 1.

    so... y = m*x +b

    once you have m (just sub in x = 1 into the derivative of y (y')) you can set x and y to 1 and -2 in your y = mx+b equation and then solve for b.

    Now that you have the equation of the line, check what x is equal to when you set y = 0;

    this will give you the a value

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