Math Problem Statement

Let f(x) =(x−3/2)/(x^2 + 2) and g(x) =(x^2+1)/(x^2 + 2). At what values of x do the curves y = f(x) and

y = g(x) have parallel tangent lines?

Solution

To find the values of xx where the curves y=f(x)y = f(x) and y=g(x)y = g(x) have parallel tangent lines, we need to compute the derivatives of f(x)f(x) and g(x)g(x), and then solve for xx such that the derivatives are equal, i.e.,

f(x)=g(x)f'(x) = g'(x)

Step 1: Differentiate f(x)f(x)

Given f(x)=x32x2+2f(x) = \frac{x - \frac{3}{2}}{x^2 + 2}, we can apply the quotient rule:

f(x)=(x2+2)(ddx(x32))(x32)ddx(x2+2)(x2+2)2f'(x) = \frac{(x^2 + 2) \cdot \left( \frac{d}{dx}(x - \frac{3}{2}) \right) - (x - \frac{3}{2}) \cdot \frac{d}{dx}(x^2 + 2)}{(x^2 + 2)^2}

Simplifying the derivatives in the numerator: f(x)=(x2+2)1(x32)2x(x2+2)2f'(x) = \frac{(x^2 + 2) \cdot 1 - (x - \frac{3}{2}) \cdot 2x}{(x^2 + 2)^2}

f(x)=x2+22x(x32)(x2+2)2f'(x) = \frac{x^2 + 2 - 2x(x - \frac{3}{2})}{(x^2 + 2)^2}

Expanding and simplifying: f(x)=x2+22x2+3x(x2+2)2f'(x) = \frac{x^2 + 2 - 2x^2 + 3x}{(x^2 + 2)^2} f(x)=x2+3x+2(x2+2)2f'(x) = \frac{-x^2 + 3x + 2}{(x^2 + 2)^2}

Step 2: Differentiate g(x)g(x)

Similarly, for g(x)=x2+1x2+2g(x) = \frac{x^2 + 1}{x^2 + 2}, we apply the quotient rule:

g(x)=(x2+2)ddx(x2+1)(x2+1)ddx(x2+2)(x2+2)2g'(x) = \frac{(x^2 + 2) \cdot \frac{d}{dx}(x^2 + 1) - (x^2 + 1) \cdot \frac{d}{dx}(x^2 + 2)}{(x^2 + 2)^2}

Simplifying the derivatives in the numerator: g(x)=(x2+2)2x(x2+1)2x(x2+2)2g'(x) = \frac{(x^2 + 2) \cdot 2x - (x^2 + 1) \cdot 2x}{(x^2 + 2)^2} g(x)=2x(x2+2)2x(x2+1)(x2+2)2g'(x) = \frac{2x(x^2 + 2) - 2x(x^2 + 1)}{(x^2 + 2)^2}

Simplifying further: g(x)=2x(x2+2x21)(x2+2)2g'(x) = \frac{2x(x^2 + 2 - x^2 - 1)}{(x^2 + 2)^2} g(x)=2x(1)(x2+2)2=2x(x2+2)2g'(x) = \frac{2x(1)}{(x^2 + 2)^2} = \frac{2x}{(x^2 + 2)^2}

Step 3: Solve f(x)=g(x)f'(x) = g'(x)

Now, we equate f(x)f'(x) and g(x)g'(x):

x2+3x+2(x2+2)2=2x(x2+2)2\frac{-x^2 + 3x + 2}{(x^2 + 2)^2} = \frac{2x}{(x^2 + 2)^2}

Since both sides have the same denominator, we can set the numerators equal:

x2+3x+2=2x-x^2 + 3x + 2 = 2x

Simplifying the equation:

x2+3x+22x=0-x^2 + 3x + 2 - 2x = 0 x2+x+2=0-x^2 + x + 2 = 0

Multiplying through by -1 to simplify:

x2x2=0x^2 - x - 2 = 0

Step 4: Solve the quadratic equation

We now solve x2x2=0x^2 - x - 2 = 0 using factoring:

(x2)(x+1)=0(x - 2)(x + 1) = 0

So, x=2x = 2 or x=1x = -1.

Conclusion:

The curves y=f(x)y = f(x) and y=g(x)y = g(x) have parallel tangent lines at x=2x = 2 and x=1x = -1.

Would you like more details on the steps? Here are 5 related questions you can explore:

  1. How do you apply the quotient rule in calculus?
  2. What does it mean for two functions to have parallel tangent lines?
  3. How can you verify if the solutions x=2x = 2 and x=1x = -1 are correct graphically?
  4. What are other methods to solve quadratic equations?
  5. Can two curves have multiple points where their tangent lines are parallel?

Tip: Understanding the geometric interpretation of derivatives can greatly help in visualizing problems involving slopes and tangents.

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Math Problem Analysis

Mathematical Concepts

Calculus
Derivatives
Quotient Rule
Tangent Lines
Quadratic Equations

Formulas

Quotient Rule: (u/v)' = (v*u' - u*v') / v^2
Quadratic Equation: ax^2 + bx + c = 0

Theorems

Quotient Rule in Calculus
Quadratic Equation Theorem

Suitable Grade Level

Grades 11-12 (Advanced High School Calculus)