Question

Find the extreme values of the function on the given interval. \(f(x)=x^{2}+x+4\) on [-1,2]

Short answer

Minimum is 3.75 and maximum is 10 on [-1, 2].

Step-by-step solution

Find the Critical Points

First, we need to find the derivative of the function to determine the critical points. The function is given by: \[ f(x) = x^2 + x + 4 \]The derivative is: \[ f'(x) = 2x + 1 \]To find the critical points, set the derivative equal to zero and solve for \(x\): \[ 2x + 1 = 0 \]\[ 2x = -1 \]\[ x = -\frac{1}{2} \]So, \(x = -\frac{1}{2}\) is a critical point.

Check Endpoints and Critical Points

The next step is to evaluate the function at the critical point and the endpoints of the interval \([-1, 2]\).**Evaluate at Critical Point**: \[ f\left(-\frac{1}{2}\right) = \left( -\frac{1}{2} \right)^2 + \left( -\frac{1}{2} \right) + 4 = \frac{1}{4} - \frac{1}{2} + 4 = \frac{15}{4} = 3.75 \]**Evaluate at Endpoints**: At \( x = -1 \):\[ f(-1) = (-1)^2 + (-1) + 4 = 1 - 1 + 4 = 4 \]At \( x = 2 \):\[ f(2) = 2^2 + 2 + 4 = 4 + 2 + 4 = 10 \]

Key concepts

Derivatives

To understand extreme values, we first need to understand derivatives. The derivative of a function represents the rate of change of the function's value with respect to changes in the input. In simpler terms, it's a tool that helps us determine how the function behaves at different points. Think of it as the slope of the curve at any given point on the graph. For the function \( f(x) = x^2 + x + 4 \), its derivative \( f'(x) = 2x + 1 \) represents this rate of change.

Why do we need the derivative to find critical points? Well, critical points occur where the derivative is zero or undefined. These points are where the function potentially has peaks, valleys, or flat spots — places where the slope of the function is zero. By setting \( f'(x) = 2x + 1 \) to zero, we found the critical point \( x = -\frac{1}{2} \). This helps us in determining where an extreme value might occur.

Extreme Values

Extreme values refer to the maximum and minimum values a function takes on an interval. These can be found either at the endpoints of the interval or at critical points where the derivative equals zero. Calculating the extreme values is especially useful to understand the overall behavior of a function over a specific region.

In our example, once the critical point \( x = -\frac{1}{2} \) is identified, we evaluate the function at both the critical point and the interval's endpoints \([-1, 2]\). This gives us the values:

• At the critical point \( x = -\frac{1}{2} \): \( f\left(-\frac{1}{2}\right) = 3.75 \)
• At \( x = -1 \): \( f(-1) = 4 \)
• At \( x = 2 \): \( f(2) = 10 \)

From these evaluations, we see that the absolute minimum on the interval is at \( x = -1 \) and the absolute maximum is at \( x = 2 \).

Polynomial Functions

Polynomial functions are essential in mathematics because they are composed of terms comprised of variables raised to non-negative integer exponents. The function \( f(x) = x^2 + x + 4 \) is a quadratic polynomial, which is the simplest kind of polynomial function that can be used to model curved graphs.

Quadratic polynomials generally graph as a parabola, which can open upwards or downwards depending on the leading coefficient. In our function, \( f(x) = x^2 + x + 4 \), the parabola opens upwards since the coefficient of \( x^2 \) is positive (\( 1 \) in this case). This makes it easier to identify the extremum at the top of the parabola as possible maximums or minimums inside a given interval.

This knowledge about polynomial functions assists in predicting where the extreme values might occur and helps in finding critical points and endpoints, as calculated in earlier steps.