Math Problem Statement

Let f(x) = e^(3 - 2x) and g(x) = (3 - ln x) / 2. (a) Show that f and g are inverse to each other. (b) Find (f ∘ g)(x) in the simplest form. (c) Sketch the graphs of f and g; indicate intercepts and asymptotes. (d) Write down the number of solutions of the equation f(x) = g(x).

Solution

Let us solve the question step by step.


Part (a): Show that f(x)f(x) and g(x)g(x) are inverse functions

To verify that f(x)f(x) and g(x)g(x) are inverses, we need to show that:

  1. f(g(x))=xf(g(x)) = x
  2. g(f(x))=xg(f(x)) = x

Given functions:

  • f(x)=e32xf(x) = e^{3 - 2x}
  • g(x)=3lnx2g(x) = \frac{3 - \ln x}{2}

Step 1: Calculate f(g(x))f(g(x)): f(g(x))=f(3lnx2)=e323lnx2f(g(x)) = f\left(\frac{3 - \ln x}{2}\right) = e^{3 - 2 \cdot \frac{3 - \ln x}{2}} Simplify: e3(3lnx)=elnx=xe^{3 - (3 - \ln x)} = e^{\ln x} = x

Step 2: Calculate g(f(x))g(f(x)): g(f(x))=g(e32x)=3ln(e32x)2g(f(x)) = g\left(e^{3 - 2x}\right) = \frac{3 - \ln\left(e^{3 - 2x}\right)}{2} Simplify: ln(e32x)=32xso:g(f(x))=3(32x)2=2x2=x\ln\left(e^{3 - 2x}\right) = 3 - 2x \quad \text{so:} \quad g(f(x)) = \frac{3 - (3 - 2x)}{2} = \frac{2x}{2} = x

Thus, ff and gg are inverses of each other.


Part (b): Simplify (fg)(x)(f \circ g)(x)

We already calculated f(g(x))f(g(x)) in part (a): f(g(x))=xf(g(x)) = x Thus, (fg)(x)=x(f \circ g)(x) = x.


Part (c): Sketch the graphs of f(x)f(x) and g(x)g(x)

To sketch the graphs of f(x)=e32xf(x) = e^{3 - 2x} and g(x)=3lnx2g(x) = \frac{3 - \ln x}{2}, we need:

  1. Intercepts:

    • For f(x)f(x): When x=0,f(0)=e32(0)=e3so the y-intercept is (0,e3).\text{When } x = 0, f(0) = e^{3 - 2(0)} = e^3 \quad \text{so the y-intercept is } (0, e^3).
    • For g(x)g(x): When x=1,g(1)=3ln(1)2=302=32.\text{When } x = 1, g(1) = \frac{3 - \ln(1)}{2} = \frac{3 - 0}{2} = \frac{3}{2}. So, g(x)g(x) has a y-intercept of (1,32)(1, \frac{3}{2}).
  2. Asymptotes:

    • For f(x)=e32xf(x) = e^{3 - 2x}: As x,f(x)0(horizontal asymptote at y=0).\text{As } x \to \infty, f(x) \to 0 \quad \text{(horizontal asymptote at } y = 0\text{)}.
    • For g(x)=3lnx2g(x) = \frac{3 - \ln x}{2}: As x0+,lnx,g(x).\text{As } x \to 0^+, \ln x \to -\infty, \quad g(x) \to \infty. As x,lnx,g(x).\text{As } x \to \infty, \ln x \to \infty, \quad g(x) \to -\infty.
  3. Behavior:

    • f(x)f(x) is an exponential decay function.
    • g(x)g(x) is a logarithmic function reflected and shifted.

Part (d): Number of solutions to f(x)=g(x)f(x) = g(x)

To solve f(x)=g(x)f(x) = g(x), we equate the two functions: e32x=3lnx2e^{3 - 2x} = \frac{3 - \ln x}{2} This equation cannot be solved algebraically, but we can analyze the graphs to determine the number of intersections.

  • f(x)=e32xf(x) = e^{3 - 2x} is strictly decreasing.
  • g(x)=3lnx2g(x) = \frac{3 - \ln x}{2} decreases for x>1x > 1.

There will likely be one solution as the graphs intersect only once based on their behavior.


Would you like a detailed graph or further clarification on any part?


Questions to Expand Understanding:

  1. How can you use the derivative to confirm that f(x)f(x) and g(x)g(x) intersect only once?
  2. What happens to the inverses of f(x)f(x) and g(x)g(x) when transformations are applied?
  3. Can you calculate the intersection point f(x)=g(x)f(x) = g(x) numerically?
  4. Why is lnx\ln x undefined for x0x \leq 0, and how does this impact g(x)g(x)?
  5. How do horizontal asymptotes affect the behavior of f(x)f(x)?

Tip:

For exponential and logarithmic functions, always check their domains and asymptotes carefully before solving equations or graphing.

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Math Problem Analysis

Mathematical Concepts

Exponential functions
Logarithmic functions
Inverse functions
Graphing
Intersections

Formulas

f(x) = e^(3 - 2x)
g(x) = (3 - ln x) / 2
f(g(x)) = x
g(f(x)) = x

Theorems

Inverse function property: f(g(x)) = g(f(x)) = x
Exponential and logarithmic relationships

Suitable Grade Level

Grades 11-12