What are two conditions to find the zeros of a quadratic function

Question

what are two conditions when it would be useful to use the quadratic formula to find the zeros of a quadratic function?

Answer 1

To find the zeros, you can: 

Use the quadratic formula, complete the square, or factor. 

It is useful to find the zeros if the function cannot be factored as (x-a)(x-b)

or if it is not of the form (x-a)(x+a).