For the function f(x) = 2x^3 - 9x^2 + 12x, find the intervals of increase. (2022

Practice Questions

Q1
For the function f(x) = 2x^3 - 9x^2 + 12x, find the intervals of increase. (2022)
  1. (-∞, 0)
  2. (0, 3)
  3. (3, ∞)
  4. (0, 2)

Questions & Step-by-Step Solutions

For the function f(x) = 2x^3 - 9x^2 + 12x, find the intervals of increase. (2022)
  • Step 1: Start with the function f(x) = 2x^3 - 9x^2 + 12x.
  • Step 2: Find the derivative of the function, f'(x). This tells us the slope of the function.
  • Step 3: Calculate the derivative: f'(x) = 6x^2 - 18x + 12.
  • Step 4: Set the derivative equal to zero to find critical points: 6x^2 - 18x + 12 = 0.
  • Step 5: Simplify the equation by dividing everything by 6: x^2 - 3x + 2 = 0.
  • Step 6: Factor the quadratic equation: (x - 1)(x - 2) = 0.
  • Step 7: Solve for x to find critical points: x = 1 and x = 2.
  • Step 8: Identify the intervals to test: (-∞, 1), (1, 2), and (2, ∞).
  • Step 9: Choose a test point in each interval and plug it into f'(x) to see if it's positive (increasing) or negative (decreasing).
  • Step 10: For the interval (-∞, 1), test x = 0: f'(0) = 12 (positive, so increasing).
  • Step 11: For the interval (1, 2), test x = 1.5: f'(1.5) = -1.5 (negative, so decreasing).
  • Step 12: For the interval (2, ∞), test x = 3: f'(3) = 12 (positive, so increasing).
  • Step 13: Combine the results: The function is increasing on the intervals (0, 1) and (2, ∞).
  • Derivative and Critical Points – Understanding how to find the derivative of a function to identify critical points where the function may change from increasing to decreasing or vice versa.
  • Test Intervals – Using test intervals around critical points to determine where the function is increasing or decreasing.
  • Function Behavior – Analyzing the behavior of polynomial functions to determine intervals of increase and decrease.
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