Math Problem Statement

Реши задание

Выберите среди предложенных интервалов монотонного возрастания функции y = (x^2 - 3)e^(5 - x).

Solution

Let's analyze the task step by step and solve it.

Task Breakdown:

  1. The original problem asks to find intervals where the function y=(x23)e5xy = (x^2 - 3)e^{5 - x} is increasing.

    • We must determine the monotonic behavior of the function y(x)y(x).
  2. Steps:

    • Find the derivative y(x)y'(x) to determine where y(x)y(x) is increasing or decreasing.
    • Solve y(x)>0y'(x) > 0 for increasing intervals.
    • Use the provided intervals to identify valid monotonicity regions.

Step 1: Find the derivative y(x)y'(x)

The function is y=(x23)e5xy = (x^2 - 3)e^{5 - x}. Applying the product rule:

[ y'(x) = \frac{d}{dx}[(x^2 - 3)] \cdot e^{5 - x} + (x^2 - 3) \cdot \frac{d}{dx}[e^{5 - x}] ]

  • The derivative of x23x^2 - 3 is 2x2x.
  • The derivative of e5xe^{5 - x} is e5x-e^{5 - x} (chain rule).

Substitute these into the product rule:

y(x)=2xe5x+(x23)(e5x)y'(x) = 2x e^{5 - x} + (x^2 - 3)(-e^{5 - x})

Factor out e5xe^{5 - x}:

y(x)=e5x[2x(x23)]y'(x) = e^{5 - x} \big[ 2x - (x^2 - 3) \big]

Simplify the term in brackets:

y(x)=e5x[x2+2x+3]y'(x) = e^{5 - x} \big[ -x^2 + 2x + 3 \big]

Thus:

y(x)=e5x(x2+2x+3)y'(x) = e^{5 - x} (-x^2 + 2x + 3)


Step 2: Analyze y(x)y'(x)

  • The term e5x>0e^{5 - x} > 0 for all xx because the exponential function is always positive. Therefore, the sign of y(x)y'(x) depends on the quadratic expression x2+2x+3-x^2 + 2x + 3.
  • Factorize x2+2x+3-x^2 + 2x + 3: x2+2x+3=(x22x3)-x^2 + 2x + 3 = -(x^2 - 2x - 3) Factor the quadratic: x22x3=(x3)(x+1)x^2 - 2x - 3 = (x - 3)(x + 1) Thus: x2+2x+3=(x3)(x+1)-x^2 + 2x + 3 = -(x - 3)(x + 1)

So: y(x)=e5x(x3)(x+1)y'(x) = e^{5 - x} \cdot -(x - 3)(x + 1)


Step 3: Solve y(x)>0y'(x) > 0

The derivative y(x)>0y'(x) > 0 when (x3)(x+1)>0-(x - 3)(x + 1) > 0.

  • Analyze the inequality (x3)(x+1)>0-(x - 3)(x + 1) > 0: (x3)(x+1)<0(x - 3)(x + 1) < 0
  • Solve (x3)(x+1)<0(x - 3)(x + 1) < 0 using a sign chart:
    • The critical points are x=1x = -1 and x=3x = 3.
    • Test intervals:
      • For x<1x < -1: (x3)(x+1)>0(x - 3)(x + 1) > 0 (negative result).
      • For 1<x<3-1 < x < 3: (x3)(x+1)<0(x - 3)(x + 1) < 0 (positive result).
      • For x>3x > 3: (x3)(x+1)>0(x - 3)(x + 1) > 0 (negative result).

Thus, y(x)>0y'(x) > 0 on (1,3)(-1, 3).


Step 4: Compare with the given intervals

The problem asks to select intervals where y(x)y(x) is increasing:

  • (3,2)(-3, -2): Not in (1,3)(-1, 3).
  • (0,1)(0, 1): Lies within (1,3)(-1, 3), so it is correct.
  • (2,3)(2, 3): Lies within (1,3)(-1, 3), so it is correct.

Final Answer:

The intervals where y(x)y(x) is increasing are:

(0,1)and(2,3)(0, 1) \quad \text{and} \quad (2, 3)

Would you like me to explain any steps in more detail?

Here are 5 related questions for further understanding:

  1. How do we interpret the signs of the derivative to determine increasing/decreasing behavior?
  2. What is the significance of factoring the quadratic in the derivative?
  3. How do we use a sign chart to solve inequalities?
  4. Why is e5xe^{5 - x} always positive, and how does it affect the derivative?
  5. How can we determine critical points for non-polynomial functions?

Tip: Always check the domain of your function and derivative before analyzing monotonic behavior.

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Math Problem Analysis

Mathematical Concepts

Calculus
Monotonicity
Derivative Analysis
Quadratic Factorization
Inequalities

Formulas

Product Rule for Derivatives: (uv)' = u'v + uv'
Chain Rule for Exponential Derivatives: (e^f(x))' = f'(x)e^f(x)
Quadratic Factorization: ax^2 + bx + c = a(x - r1)(x - r2)

Theorems

Sign of the Derivative Theorem: A function is increasing when its derivative is positive.

Suitable Grade Level

Grades 10-12