Math Problem Statement

Let f(x) = x + |x|. (a) Using the definition of the derivative, find f'(2). (b) Find an equation of the tangent line to f at x = 2.

Solution

Let's address the questions in the image.

The function given is f(x)=x+xf(x) = x + |x|.

Part (a): Using the definition of the derivative, find f(2)f'(2).

The definition of the derivative is:

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

For f(x)=x+xf(x) = x + |x|, we must first understand how the absolute value affects the derivative. The function behaves differently depending on whether xx is positive or negative:

  • For x0x \geq 0, f(x)=x+x=2xf(x) = x + x = 2x.
  • For x<0x < 0, f(x)=xx=0f(x) = x - x = 0.

Since x=2x = 2 is positive, the derivative will be calculated using the expression for x0x \geq 0, i.e., f(x)=2xf(x) = 2x.

Now, applying the definition of the derivative at x=2x = 2:

f(2)=limh0f(2+h)f(2)hf'(2) = \lim_{h \to 0} \frac{f(2+h) - f(2)}{h}

Substituting f(2+h)=2(2+h)=4+2hf(2+h) = 2(2+h) = 4 + 2h and f(2)=4f(2) = 4:

f(2)=limh0(4+2h)4h=limh02hh=2f'(2) = \lim_{h \to 0} \frac{(4 + 2h) - 4}{h} = \lim_{h \to 0} \frac{2h}{h} = 2

Thus, f(2)=2f'(2) = 2.

Part (b): Find an equation of the tangent line to ff at x=2x = 2.

The equation of a tangent line is given by:

yf(a)=f(a)(xa)y - f(a) = f'(a)(x - a)

We already know that f(2)=2f'(2) = 2 and we can find f(2)f(2) using the function f(x)=2xf(x) = 2x for x0x \geq 0:

f(2)=2(2)=4f(2) = 2(2) = 4

Therefore, the equation of the tangent line at x=2x = 2 is:

y4=2(x2)y - 4 = 2(x - 2)

Simplifying:

y=2x4+4    y=2xy = 2x - 4 + 4 \implies y = 2x

So, the equation of the tangent line is y=2xy = 2x.


Would you like further clarification on any of these steps? Here are 5 related questions for further understanding:

  1. How does the definition of the derivative work when applied to non-linear functions?
  2. What would happen if we calculated the derivative at x=2x = -2?
  3. Can you describe the behavior of f(x)=x+xf(x) = x + |x| for negative values of xx?
  4. How does the absolute value affect the differentiability of a function?
  5. How would the tangent line change if x=3x = 3 instead of x=2x = 2?

Tip: When working with absolute value functions, always consider the behavior of the function separately in different regions (positive and negative parts).

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Math Problem Analysis

Mathematical Concepts

Calculus
Absolute Value Functions
Derivatives
Tangent Lines

Formulas

f'(x) = lim(h -> 0) [(f(x + h) - f(x)) / h]
Equation of a tangent line: y - f(a) = f'(a)(x - a)

Theorems

Definition of the derivative

Suitable Grade Level

Grades 11-12 (Pre-Calculus/Calculus)