Math Problem Statement

Use the limit definition of the derivative to find f'(x) if f(x) = 1/(3x+2)

Solution

To find the derivative of the function f(x)=13x+2f(x) = \frac{1}{3x+2} using the limit definition of the derivative, we proceed as follows:

Step 1: Write the Limit Definition of the Derivative

The derivative of f(x)f(x) at any point xx is given by:

f(x)=limh0f(x+h)f(x)hf'(x) = \lim_{h \to 0} \frac{f(x+h) - f(x)}{h}

Step 2: Substitute the Function into the Definition

We know f(x)=13x+2f(x) = \frac{1}{3x+2}. So, we first need to find f(x+h)f(x+h):

f(x+h)=13(x+h)+2=13x+3h+2f(x+h) = \frac{1}{3(x+h) + 2} = \frac{1}{3x + 3h + 2}

Now, substitute f(x+h)f(x+h) and f(x)f(x) into the limit definition:

f(x)=limh013x+3h+213x+2hf'(x) = \lim_{h \to 0} \frac{\frac{1}{3x + 3h + 2} - \frac{1}{3x + 2}}{h}

Step 3: Simplify the Expression

To simplify the expression, combine the two fractions in the numerator:

f(x)=limh0(3x+2)(3x+3h+2)(3x+3h+2)(3x+2)hf'(x) = \lim_{h \to 0} \frac{\frac{(3x + 2) - (3x + 3h + 2)}{(3x + 3h + 2)(3x + 2)}}{h}

Simplify the numerator:

f(x)=limh03x+23x3h2(3x+3h+2)(3x+2)h=limh03h(3x+3h+2)(3x+2)hf'(x) = \lim_{h \to 0} \frac{\frac{3x + 2 - 3x - 3h - 2}{(3x + 3h + 2)(3x + 2)}}{h} = \lim_{h \to 0} \frac{\frac{-3h}{(3x + 3h + 2)(3x + 2)}}{h}

Simplify further by canceling hh in the numerator and denominator:

f(x)=limh03(3x+3h+2)(3x+2)f'(x) = \lim_{h \to 0} \frac{-3}{(3x + 3h + 2)(3x + 2)}

Step 4: Evaluate the Limit

Finally, take the limit as hh approaches 0:

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

So, the derivative of f(x)=13x+2f(x) = \frac{1}{3x+2} is:

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

Would you like more details, or do you have any questions?

Here are 8 related questions you might consider:

  1. How would the derivative change if f(x)=15x+3f(x) = \frac{1}{5x+3}?
  2. What is the derivative of f(x)=13x+2f(x) = \frac{1}{3x+2} using the chain rule?
  3. How can you apply the limit definition to find the second derivative of f(x)=13x+2f(x) = \frac{1}{3x+2}?
  4. Can you find the derivative of f(x)=13x+2f(x) = \frac{1}{3x+2} using the quotient rule?
  5. How does the concept of limits apply to the continuity of f(x)=13x+2f(x) = \frac{1}{3x+2}?
  6. What is the significance of the negative sign in the derivative f(x)=3(3x+2)2f'(x) = \frac{-3}{(3x+2)^2}?
  7. How would you interpret the graph of the derivative function f(x)f'(x)?
  8. Can you find the derivative of a similar function, such as f(x)=1x2+1f(x) = \frac{1}{x^2 + 1}?

Tip: When using the limit definition of the derivative, always ensure to simplify the expression before taking the limit for easier calculation.

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Math Problem Analysis

Mathematical Concepts

Calculus
Derivatives
Limit Definition of Derivative

Formulas

Limit definition of the derivative

Theorems

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Suitable Grade Level

Advanced High School or College