This question is testing one's ability to analyze a function algebraically and graphically and identify the vertex of a function. Identifying properties of functions through analyzing equivalent forms is critical to this concept. Such properties that can be found through analyzing the different forms of a function include finding roots (zeros), extreme values, symmetry, and intercepts. 

For the purpose of Common Core Standards, finding the line of symmetry falls within the Cluster C of analyze functions using different representations concept (CCSS.Math.content.HSF-IF.C.8). 

Knowing the standard and the concept for which it relates to, we can now do the step-by-step process to solve the problem in question.

Step 1: Use technology to graph the function.

Step 2: Recognize the formula for calculating the vertex of a parabola.

The  coordinate of the vertex can be found using the following formula.

Substituting in the values for this particular function results in the following.

Step 3: Verify by graphing that the  value in the function's vertex represents the line of symmetry.

Therefore, the line of symmetry occurs at .

This question is testing one's ability to analyze a function algebraically and recognize different but equivalent forms. Identifying properties of functions through analyzing equivalent forms is critical to this concept. Such properties that can be found through analyzing the different forms of a function include finding roots (zeros), extreme values, symmetry, and intercepts.

For the purpose of Common Core Standards, using factoring falls within the Cluster C of analyze functions using different representations concept (CCSS.Math.content.HSF-IF.C.8). 

Knowing the standard and the concept for which it relates to, we can now do the step-by-step process to solve the problem in question.

Step 1: Recognize the form that the function is given in.

Recall the standard form of a quadratic is,

.

Step 2: Recognize the factored form of the original function.

Recall the factored form of a quadratic is,

where  and  are factors of  and  and  are factors of  for which,

Step 3: Verify result.

Using the above steps for this particular problem looks as follows.

Step 1: Recognize the form that the function is given in.

therefore,

Step 2: Recognize the factored form of the original function.

First, identify the factors of  and .

From here find the factors of  that when added together result in .

Therefore the factored form of the function would be as follows.

Step 3: Verify result.

To verify that the factored form is equivalent to the original function, multiply the binomials together using the distributive property of each term to each other. To accomplish this multiply the first terms together, then multiply the outer terms together, then the inner terms, and finally the last terms. Once the multiplication has occurred, combine like terms to simplify.