No, not all global extrema are also local extrema of polynomial functions. A global extremum is a point where the function has the highest or lowest value over its entire domain, while a local extremum is a point where the function has the highest or lowest value in a specific neighborhood. A polynomial function can have global extrema that are not local extrema if the function continues to increase or decrease beyond the neighborhood of the extremum. **

Local extrema are the highest or lowest points within a specific interval or neighborhood of a function, while global extrema are the highest or lowest points of the entire function. In other words, local extrema are relative to a specific region of the function, while global extrema are absolute and apply to the entire function. Local extrema can occur at points where the derivative of the function is zero or undefined, while global extrema occur at the endpoints of the interval or at critical points within the interval. **

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Extrema of a function can be determined by finding the critical points where the derivative is equal to zero or undefined. These critical points are then evaluated to determine if they correspond to a maximum or minimum value. Additionally, the endpoints of the interval being considered should also be checked to see if they are extrema. By analyzing the critical points and endpoints, one can determine the extrema of a function. **

Local extrema are points on a graph where a function reaches a maximum or minimum value within a specific interval. A local maximum is the highest point in a small neighborhood of a function, while a local minimum is the lowest point in that neighborhood. These points are called "local" because they may not be the absolute highest or lowest points of the entire function, but rather within a limited range. **

Extrema are determined by finding the critical points of a function, which are points where the derivative is either zero or undefined. To find these critical points, we set the derivative of the function equal to zero and solve for the variable. We then evaluate the function at these critical points as well as at the endpoints of the interval of interest to determine the maximum and minimum values. The highest value among these points is the maximum (if it exists), and the lowest value is the minimum (if it exists). **

Global extrema occur at the highest or lowest points of a function over its entire domain. For a function to have a global maximum, the value of the function at that point must be greater than or equal to the value of the function at all other points in its domain. Similarly, for a function to have a global minimum, the value of the function at that point must be less than or equal to the value of the function at all other points in its domain. **

Boundary extrema are not always present in all situations. In some cases, there may be a continuous range of values without distinct boundaries, making it difficult to identify extrema. Additionally, in certain scenarios, the extrema may be located at interior points rather than at the boundaries. Therefore, the presence of boundary extrema depends on the specific context and nature of the problem being considered. **