Math Problem Statement

Given the function \( f(x) = \sqrt[3]{256x^3 + 256} \), find the equation of the tangent line at \( x = 1 \), use it to approximate \( f(1.1) \), and compute the error between \( f(1.1) \) and the approximation.

Solution

Let's work through the problem step by step.

Given function:

f(x)=256x3+2563f(x) = \sqrt[3]{256x^3 + 256}

Step 1: Find the equation of the tangent line to the graph of the function at x=1x = 1.

To find the equation of the tangent line, we need to use the formula for the equation of a line: L(x)=f(x0)(xx0)+f(x0)L(x) = f'(x_0)(x - x_0) + f(x_0) where x0=1x_0 = 1, f(x)f'(x) is the derivative of the function, and f(x0)f(x_0) is the function value at x=1x = 1.

  1. Calculate f(1)f(1): [ f(1) = \sqrt[3]{256(1)^3 + 256} = \sqrt[3]{512} = 8 ]

  2. Find f(x)f'(x) (the derivative of the function):

    • Apply the chain rule to differentiate f(x)=256x3+2563f(x) = \sqrt[3]{256x^3 + 256}.

f(x)=ddx((256x3+256)1/3)=13(256x3+256)2/3(768x2)f'(x) = \frac{d}{dx}\left( (256x^3 + 256)^{1/3} \right) = \frac{1}{3}(256x^3 + 256)^{-2/3} \cdot (768x^2) f(x)=768x23(256x3+256)2/3=256x2(256x3+256)2/3f'(x) = \frac{768x^2}{3(256x^3 + 256)^{2/3}} = \frac{256x^2}{(256x^3 + 256)^{2/3}}

  1. Evaluate f(1)f'(1): f(1)=256(1)2(256(1)3+256)2/3=2565122/3=25664=4f'(1) = \frac{256(1)^2}{(256(1)^3 + 256)^{2/3}} = \frac{256}{512^{2/3}} = \frac{256}{64} = 4

Now that we have f(1)=8f(1) = 8 and f(1)=4f'(1) = 4, the equation of the tangent line is: L(x)=4(x1)+8L(x) = 4(x - 1) + 8 Simplifying: L(x)=4x4+8=4x+4L(x) = 4x - 4 + 8 = 4x + 4

Step 2: Use the tangent line to approximate f(1.1)f(1.1).

Using the equation of the tangent line L(x)=4x+4L(x) = 4x + 4, we can approximate f(1.1)f(1.1) by calculating L(1.1)L(1.1): L(1.1)=4(1.1)+4=4.4+4=8.4L(1.1) = 4(1.1) + 4 = 4.4 + 4 = 8.4

Step 3: Compute the actual value of f(1.1)f(1.1) and find the error.

  1. Actual value of f(1.1)f(1.1): [ f(1.1) = \sqrt[3]{256(1.1)^3 + 256} = \sqrt[3]{256(1.331) + 256} = \sqrt[3]{340.736 + 256} = \sqrt[3]{596.736} \approx 8.37866 ]

  2. Calculate the error: Error=f(1.1)L(1.1)=8.378668.4=0.02134\text{Error} = |f(1.1) - L(1.1)| = |8.37866 - 8.4| = 0.02134

Final Answers:

  • Equation of the tangent line: L(x)=4x+4L(x) = 4x + 4
  • Approximation of f(1.1)f(1.1) using the tangent line: L(1.1)=8.4L(1.1) = 8.4
  • Actual value of f(1.1)f(1.1): f(1.1)8.37866f(1.1) \approx 8.37866
  • Error: 0.02134\approx 0.02134

Do you need further details or explanations? Here are some follow-up questions you might find useful:

  1. How is the chain rule applied when differentiating functions involving cube roots?
  2. What is the significance of the tangent line in approximating values of the function?
  3. How would the tangent line approximation change if the function's curvature was different at x=1x = 1?
  4. Can the error between the approximation and the actual value be reduced, and how?
  5. What other methods could be used to approximate f(1.1)f(1.1) besides using a tangent line?

Tip: For better accuracy in approximations, the second derivative (concavity) can sometimes be considered, leading to a quadratic approximation.

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Math Problem Analysis

Mathematical Concepts

Calculus
Derivatives
Linear Approximation
Error Calculation

Formulas

Equation of the tangent line: \( L(x) = f'(x_0)(x - x_0) + f(x_0) \)
Derivative of a cube root function using the chain rule
Error formula: \( |f(x) - L(x)| \)

Theorems

Chain Rule

Suitable Grade Level

Grades 11-12