Math Problem Statement

Find the area of the region described. The region bounded by yequalse Superscript x​, yequals3 e Superscript negative x Baseline plus 2​, and xequals0

Solution

We are asked to find the area of the region bounded by the curves:

  1. y=exy = e^x
  2. y=3ex+2y = 3e^{-x} + 2
  3. x=0x = 0 (the vertical line at x=0x = 0).

To find the area between the curves, we need to follow these steps:

Step 1: Find the points of intersection

The region is bounded between the two curves, so we need to find where the curves intersect. Set the two equations equal to each other to find the xx-coordinates of the points of intersection:

ex=3ex+2e^x = 3e^{-x} + 2

Multiply both sides of the equation by exe^x to eliminate the negative exponent:

e2x=3+2exe^{2x} = 3 + 2e^x

This is a quadratic equation in exe^x. Let u=exu = e^x, so the equation becomes:

u2=3+2uu^2 = 3 + 2u

Rearranging:

u22u3=0u^2 - 2u - 3 = 0

We can solve this quadratic equation using the quadratic formula:

u=(2)±(2)24(1)(3)2(1)u = \frac{-(-2) \pm \sqrt{(-2)^2 - 4(1)(-3)}}{2(1)}

u=2±4+122u = \frac{2 \pm \sqrt{4 + 12}}{2}

u=2±162u = \frac{2 \pm \sqrt{16}}{2}

u=2±42u = \frac{2 \pm 4}{2}

Thus, the two solutions are:

u=2+42=3oru=242=1u = \frac{2 + 4}{2} = 3 \quad \text{or} \quad u = \frac{2 - 4}{2} = -1

Since u=exu = e^x and exe^x is always positive, we discard u=1u = -1. Therefore, u=3u = 3, which means ex=3e^x = 3, and thus:

x=ln3x = \ln 3

Step 2: Set up the integral

Now we know that the curves intersect at x=0x = 0 and x=ln3x = \ln 3. To find the area between the curves, we integrate the difference between the two functions from x=0x = 0 to x=ln3x = \ln 3:

Area=0ln3[(3ex+2)ex]dx\text{Area} = \int_0^{\ln 3} \left[ (3e^{-x} + 2) - e^x \right] \, dx

Step 3: Simplify the integrand

The integrand is:

(3ex+2)ex=3ex+2ex(3e^{-x} + 2) - e^x = 3e^{-x} + 2 - e^x

Thus, the area is:

Area=0ln3(3exex+2)dx\text{Area} = \int_0^{\ln 3} (3e^{-x} - e^x + 2) \, dx

Step 4: Solve the integral

Now, we integrate each term individually:

3exdx=3ex\int 3e^{-x} \, dx = -3e^{-x} exdx=ex\int -e^x \, dx = -e^x 2dx=2x\int 2 \, dx = 2x

Therefore:

Area=[3exex+2x]0ln3\text{Area} = \left[ -3e^{-x} - e^x + 2x \right]_0^{\ln 3}

Step 5: Evaluate the integral

Substitute the limits of integration:

At x=ln3x = \ln 3:

3eln3eln3+2(ln3)-3e^{-\ln 3} - e^{\ln 3} + 2(\ln 3) Since eln3=3e^{\ln 3} = 3 and eln3=13e^{-\ln 3} = \frac{1}{3}:

3×133+2ln3=13+2ln3=4+2ln3-3 \times \frac{1}{3} - 3 + 2\ln 3 = -1 - 3 + 2\ln 3 = -4 + 2\ln 3

At x=0x = 0:

3e0e0+2(0)=31=4-3e^{0} - e^{0} + 2(0) = -3 - 1 = -4

Now, subtract the value at x=0x = 0 from the value at x=ln3x = \ln 3:

Area=(4+2ln3)(4)=2ln3\text{Area} = \left( -4 + 2\ln 3 \right) - (-4) = 2\ln 3

Final Answer:

The area of the region is 2ln3\boxed{2\ln 3}.


Would you like a more detailed explanation or any clarification? Also, here are some related questions:

  1. How would the area change if the curves were shifted vertically or horizontally?
  2. How do you handle integrals involving more complex functions, such as logarithms or trigonometric functions?
  3. What other methods are available to find the area between curves (e.g., numerical methods)?
  4. How would you approach finding the volume of a region bounded by similar curves in three dimensions?
  5. How do you use the method of integration by parts in these types of problems?

Tip: When solving for the area between curves, always check the points of intersection to ensure your integral limits are correct!

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Math Problem Analysis

Mathematical Concepts

Calculus
Definite Integrals
Area between curves
Exponential functions
Logarithms

Formulas

Area = ∫[a, b] (f(x) - g(x)) dx
Exponential equation: e^x
Logarithmic equation: ln(x)

Theorems

Fundamental Theorem of Calculus
Quadratic formula

Suitable Grade Level

Grades 11-12