Rogelio is asked to sketch a graph of g(x)=3x^3(x−5)^2(5−x)^4 . How many turning points should his sketch include?

1 answer

To find out how many turning points the function \( g(x) = 3x^3(x-5)^2(5-x)^4 \) has, we need to determine the derivative of the function and analyze its critical points.

  1. Find the degree of the polynomial: The expression consists of several factors:
    • \( 3x^3 \) contributes a degree of 3.
    • \( (x - 5)^2 \) contributes a degree of 2.
    • \( (5 - x)^4 \) contributes a degree of 4.

Combining these, the total degree of \( g(x) \) is: \[ 3 + 2 + 4 = 9 \]

  1. The maximum number of turning points: The maximum number of turning points in a polynomial function is \( n-1 \), where \( n \) is the degree of the polynomial. For our polynomial, which is of degree 9, the maximum number of turning points is: \[ 9 - 1 = 8 \]

  2. Multiplicity of roots and their effects: To accurately count the turning points, we need to consider the roots of \( g(x) \) and their multiplicities:

    • The function has roots at \( x = 0 \) (multiplicity 3), \( x = 5 \) (multiplicity 2), and \( x = 5 \) (from \( (5-x)^4 \), which is the same point, contributing a total of \( 4 \) more).

    • Thus, the roots of \( g(x) \) and their total multiplicities are:

      • \( x = 0 \): multiplicity 3 (thus contributes only 2 turning points, as turning points occur only at odd multiplicities).
      • \( x = 5 \): multiplicity 2 (does not contribute a turning point).
      • \( (5-x)^4 \) at \( x=5 \): contributes no additional turning points.
  3. Analyzing contributions: The effective multiplicities show that:

    • At \( x=0 \), with a multiplicity of 3, there will be 2 turning points (because an odd multiplicity results in a turning point, but the even parts indicate no additional crossing).
    • At \( x=5 \), both multiplicities (2 from \( (x-5)^2 \) and 4 from \( (5-x)^4 \)), being even, do not contribute any additional turning points.
  4. Summary: Since the only point contributing turning points is \( x=0 \) (2 turning points), we conclude:

  • Total turning points = 2.

Thus, the sketch of \( g(x) \) should include a total of 2 turning points.