Math Problem Statement

Find an equation of the tangent line for f(x) = 7 / (6 + x^2) at x = 6.

Solution

We are tasked with finding the equation of the tangent line to the function f(x)=76+x2f(x) = \frac{7}{6 + x^2} at x=6x = 6.

Steps to Solve:

  1. Find the value of f(6)f(6): This gives us the point on the curve where the tangent line touches.

    f(6)=76+62=76+36=742=16f(6) = \frac{7}{6 + 6^2} = \frac{7}{6 + 36} = \frac{7}{42} = \frac{1}{6}

  2. Find f(x)f'(x), the derivative of f(x)f(x): We'll use the quotient rule to differentiate. The quotient rule states:

    f(x)=ddx(76+x2)=(6+x2)072x(6+x2)2=14x(6+x2)2f'(x) = \frac{d}{dx} \left( \frac{7}{6 + x^2} \right) = \frac{(6 + x^2) \cdot 0 - 7 \cdot 2x}{(6 + x^2)^2} = \frac{-14x}{(6 + x^2)^2}

  3. Evaluate f(6)f'(6), the slope of the tangent line at x=6x = 6:

    f(6)=14(6)(6+62)2=84(6+36)2=84422=841764=7147=121f'(6) = \frac{-14(6)}{(6 + 6^2)^2} = \frac{-84}{(6 + 36)^2} = \frac{-84}{42^2} = \frac{-84}{1764} = -\frac{7}{147} = -\frac{1}{21}

  4. Equation of the tangent line: The equation of the tangent line is given by the point-slope form:

    yf(6)=f(6)(x6)y - f(6) = f'(6)(x - 6)

    Substituting f(6)=16f(6) = \frac{1}{6} and f(6)=121f'(6) = -\frac{1}{21}:

    y16=121(x6)y - \frac{1}{6} = -\frac{1}{21}(x - 6)

    Simplifying the equation:

    y16=121x+621=121x+27y - \frac{1}{6} = -\frac{1}{21}x + \frac{6}{21} = -\frac{1}{21}x + \frac{2}{7}

    Finally, add 16\frac{1}{6} to both sides to get the equation of the tangent line:

    y=121x+27+16y = -\frac{1}{21}x + \frac{2}{7} + \frac{1}{6}

    To combine the constants 27\frac{2}{7} and 16\frac{1}{6}, find a common denominator:

    27+16=1242+742=1942\frac{2}{7} + \frac{1}{6} = \frac{12}{42} + \frac{7}{42} = \frac{19}{42}

    Thus, the equation of the tangent line is:

    y=121x+1942y = -\frac{1}{21}x + \frac{19}{42}


Would you like further details or have any questions about this process? Here are 5 related questions you might explore:

  1. How is the quotient rule applied in general when differentiating functions?
  2. What are the alternative methods to find the slope of a tangent line?
  3. Can we always use the point-slope form to find the equation of a tangent line?
  4. How do different types of functions (e.g., polynomials or trigonometric functions) affect the shape of their tangent lines?
  5. How does the concavity of a function impact the behavior of its tangent line?

Tip: When combining fractions, always check if they can be simplified before adding, which makes calculations more manageable.

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Math Problem Analysis

Mathematical Concepts

Calculus
Derivatives
Tangent Line
Quotient Rule

Formulas

Quotient Rule: f'(x) = [g(x) * h'(x) - h(x) * g'(x)] / [h(x)]^2
Point-Slope Formula: y - y1 = m(x - x1)

Theorems

Differentiation
Quotient Rule

Suitable Grade Level

Grades 11-12, College