Problem 36 - Precalculus : Building Concepts and Connections

Question

Decide if each function is odd, even, or neither by using the definitions. $$f(x)=-3 x^{2}+1$$

Step-by-Step Solution

Answer

The function \(f(x)=-3x^{2}+1\) is an even function.

Step 1: Evaluate Function at \(-x\)

Substitute \(-x\) for \(x\) in function \(f(x)=-3x^{2}+1\), hence: \(f(-x) = -3(-x)^{2}+1\).

Step 2: Simplify the Result

Simplify the evaluated function \(f(-x)\), it simplifies to \(f(-x) = -3x^{2}+1\), which is the same as \(f(x)\).

Step 3: Compare \(f(x)\) and \(f(-x)\)

Since \(f(x) = f(-x)\), we can see that the given function is an even function as by the definition of even function, \(f(x) = f(-x)\) for all \(x\) in the function's domain. Hence, the function \(f(x)=-3x^{2}+1\) is even.

Key Concepts

Symmetry of Functions

Understanding the symmetry of a function is crucial in determining whether a function is even or odd. The symmetry refers to how the graph of a function aligns along an axis. For a function to be classified as even, its graph must be symmetrical about the y-axis. This means that if you were to fold the graph along the y-axis, both halves would match perfectly. Mathematically, a function is even if for every input value x, the output value at -x is the same, which is stated as \( f(x) = f(-x) \).

Odd functions, on the other hand, display symmetry about the origin, which means if you rotate the graph 180 degrees around the origin, you'll get the same graph. This property is captured in the equation \( f(-x) = -f(x) \) for every value of x in the domain of the function. In our example, evaluating the function at \(-x\) resulted in the same expression as the function evaluated at \(x\), indicating that the function \( f(x) = -3x^{2} + 1 \) is even due to its y-axis symmetry.

Function Evaluation

Function evaluation involves substituting a specific value for the variable x in the function's formula to determine the resulting output. In the textbook exercise, we were asked to substitute \(-x\) for \(x\) in the function \(f(x) = -3x^{2} + 1\) to evaluate \(f(-x)\). This process is an essential step in identifying the symmetry of the function. It is important to carry out the substitution carefully to ensure accuracy. In our case, \(-x\) was squared to give \(x^2\), maintaining the same sign due to the properties of exponents. This substitution led us to confirm that \(f(-x)\) is indeed identical to \(f(x)\), supporting our conclusion that the function is even.

Function evaluation is not limited to identifying symmetry; it's a fundamental tool in all aspects of mathematical analysis, enabling us to calculate outputs for a given set of inputs, thereby understanding the behavior of functions.

Simplifying Expressions

Simplifying expressions is a process that often involves combining like terms, applying algebraic rules, and reducing equations to their simplest form. It's a critical skill that can make it easier to understand and solve problems. In the context of determining if a function is even or odd, simplifying the expression after substituting \(-x\) for \(x\) can confirm whether the original function and the function evaluated at \(-x\) are the same or opposites of each other.

In our example, after substituting \(-x\), we simplified \(-3(-x)^2 + 1\) to \(-3x^2 + 1\), which was the same as the original function. This step was essential in identifying the function's even symmetry. Simplifying expressions is inherently linked with function evaluation, as we often need to simplify to evaluate functions correctly. Careful simplification is the key to accurate and meaningful results in mathematics.