There is no need for "complete the square" method.
Example 1 - mental math and shortcut
Step 1- mental math:
Eliminate answer choices that don't have a value matching the given equation.
Determine the x-coordinate of the vertex from the given equation as -b/2a. Match it to the x-coordinate of the vertex from answer choices.
In some questions, this may eliminate all 3 incorrect answer choices. If not, the remaining incorrect answer choices (usually 1 of the 2 remaining) may be eliminated using a shortcut as shown in Step 2.
Step 2 - may be shortcut and mental math depending on comfort level, otherwise use Step 2 shown in the book: It may seem confusing at first but try it to see that it is not. If a = 1, the correct answer choice may be apparent by eyeballing.
Pick one of the remaining answer choice. Square the value of h and multiply it by the value of a if a > 1. Add this number to the value of k. If it matches the value of c in the given equation it is the correct answer choice. If not, the remaining answer choice is the correct answer.
Here is the shortcut: (h squared x a) + k.