For the function f(x) = x^3 - 6x^2 + 9x, find the local minima. (2022)

Practice Questions

Q1
For the function f(x) = x^3 - 6x^2 + 9x, find the local minima. (2022)
  1. (1, 4)
  2. (2, 1)
  3. (3, 0)
  4. (0, 0)

Questions & Step-by-Step Solutions

For the function f(x) = x^3 - 6x^2 + 9x, find the local minima. (2022)
  • Step 1: Start with the function f(x) = x^3 - 6x^2 + 9x.
  • Step 2: Find the derivative of the function, which is f'(x) = 3x^2 - 12x + 9.
  • Step 3: Set the derivative equal to zero to find critical points: 3x^2 - 12x + 9 = 0.
  • Step 4: Simplify the equation by dividing everything by 3: x^2 - 4x + 3 = 0.
  • Step 5: Factor the quadratic equation: (x - 1)(x - 3) = 0.
  • Step 6: Solve for x: This gives us the critical points x = 1 and x = 3.
  • Step 7: To find if these points are local minima or maxima, we can use the second derivative test.
  • Step 8: Find the second derivative: f''(x) = 6x - 12.
  • Step 9: Evaluate the second derivative at the critical points: f''(1) = 6(1) - 12 = -6 (which is less than 0, so x = 1 is a local maximum) and f''(3) = 6(3) - 12 = 6 (which is greater than 0, so x = 3 is a local minimum).
  • Step 10: To find the value of the local minimum, calculate f(3): f(3) = 3^3 - 6(3^2) + 9(3) = 27 - 54 + 27 = 0.
  • Step 11: Therefore, the local minimum occurs at x = 3 with a value of f(3) = 0.
  • Finding Local Minima – The process of determining points where a function reaches a local minimum by analyzing its first derivative.
  • Critical Points – Points where the first derivative is zero or undefined, which are candidates for local extrema.
  • Second Derivative Test – A method to confirm whether a critical point is a local minimum, local maximum, or neither by evaluating the second derivative.
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