Answer:
See below.
Explanation:
The four main ways to solve a quadratic equation are:
1) Factoring, 2) Completing the Square, 3) Graphing, and 4) Quadratic Formula.
Each method has it's own pros and cons.
1) Factoring. You should factor when the given equation is easily factor-able or already factored. For instance:

These problems are easily factored so factoring is preferred here. However, factoring will not always work.
2) Completing the Square. You complete the square if you are able to complete the perfect square trinomial with only integers. For instance:

However, you wound't use completing the square if:

The perfect square trinomial includes fractions so you would use alternative methods here (and factoring works here!).
Despite the complexity of completing the square, if done correctly, it works every time. However, sometimes, it can be time-consuming.
3) Graphing. Graphing (if on paper) is time-consuming. You would only use graphing when you only need an approximation. Unless directed to, you probably won't need to use graphing.
However, if you have a graphing calculator, graphing the equation can allow you to check your answer. So, graphing won't get you precise answer, but it will allow you to check your answer is necessary.
4) Quadratic Formula. Use the quadratic formula if the equation isn't factor-able and completing the square is too tedious. For instance:

This doesn't seem factor-able and completing the square will take a while. Graphing won't get the exact answer, so the quadratic formula is the only avenue left.
The quadratic method, like completing the square, will always work.
Only con is that you need to memorize the formula.