Answer: When the quadratic equation can be factored or solved by completing the square, you do not need to use the quadratic formula
Step-by-step explanation: In the form ax² + bx + c
Whenever a is 1 (implied, no coefficient of x²) and the constant, c, is a multiple of numbers whose sum or difference is equal to b, factoring is much quicker and easier than using the quadratic formula.
Even when there is a coefficient of x², there are procedures to find the factors and solve for x without resorting to the quadratic formula.