Math Problem Statement

The graphs of the linear function f and the piecewise linear function g are shown in the figure above. If h(x) = f(x)g(x), then h'(3) = ?

Solution

To solve for h(3)h'(3) given h(x)=f(x)g(x)h(x) = f(x)g(x), we need to use the product rule for differentiation:

h(x)=f(x)g(x)+f(x)g(x)h'(x) = f'(x)g(x) + f(x)g'(x)

Our task is to find h(3)h'(3), which means evaluating h(x)h'(x) at x=3x = 3.

Step 1: Identify f(x)f(x) and g(x)g(x) at x=3x = 3

From the graph:

  • f(3)f(3) appears to be around 44.
  • g(3)g(3) appears to be around 22.

Step 2: Determine f(3)f'(3) and g(3)g'(3)

For f(x)f(x):

The function f(x)f(x) is linear, so it has a constant slope. Observing the line, f(x)f(x) has a negative slope. We can calculate the slope by choosing two points on the line:

  • At x=0x = 0, f(x)=7f(x) = 7.
  • At x=6x = 6, f(x)=0f(x) = 0.

The slope of f(x)f(x), or f(x)f'(x), is: f(x)=0760=76f'(x) = \frac{0 - 7}{6 - 0} = -\frac{7}{6}

Thus, f(3)=76f'(3) = -\frac{7}{6}.

For g(x)g(x):

The function g(x)g(x) is piecewise linear. At x=3x = 3, we need the slope of g(x)g(x) in the interval around x=3x = 3. Observing the line segments, between x=2x = 2 and x=4x = 4:

  • At x=2x = 2, g(x)=1g(x) = 1.
  • At x=4x = 4, g(x)=3g(x) = 3.

The slope of g(x)g(x), or g(x)g'(x), in this interval is: g(x)=3142=1g'(x) = \frac{3 - 1}{4 - 2} = 1

Thus, g(3)=1g'(3) = 1.

Step 3: Apply the Product Rule

Now we substitute these values into the product rule formula: h(3)=f(3)g(3)+f(3)g(3)h'(3) = f'(3)g(3) + f(3)g'(3)

Substituting the values: h(3)=(76)(2)+(4)(1)h'(3) = \left(-\frac{7}{6}\right)(2) + (4)(1)

Calculating each term:

  1. f(3)g(3)=76×2=73f'(3)g(3) = -\frac{7}{6} \times 2 = -\frac{7}{3}
  2. f(3)g(3)=4×1=4f(3)g'(3) = 4 \times 1 = 4

Adding these: h(3)=73+4=73+123=53h'(3) = -\frac{7}{3} + 4 = -\frac{7}{3} + \frac{12}{3} = \frac{5}{3}

Final Answer

h(3)=53h'(3) = \frac{5}{3}

Would you like further details or have any questions?


  1. How is the product rule used in this problem?
  2. Why is it necessary to calculate the slopes f(3)f'(3) and g(3)g'(3)?
  3. How do we interpret a piecewise function in derivative calculations?
  4. What are the implications if g(x)g(x) were not piecewise?
  5. Could this problem be solved using another method?

Tip: When dealing with piecewise functions, always check the interval around the point of interest to determine the correct slope.

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Math Problem Analysis

Mathematical Concepts

Differentiation
Product Rule
Piecewise Functions

Formulas

Product rule: h'(x) = f'(x)g(x) + f(x)g'(x)

Theorems

Product Rule for Differentiation

Suitable Grade Level

High School (Grades 11-12) or Early College