When do we use the quadratic formula, and when the completing the square method?

First, you have to understand that both are essentially the same; the formula is based on the completing the square method. ax^2+b^x+c=0 can with appropriate steps be transformed to x = (-b +- root(b^2-4ac))/2a. The general rule of thumb for when to use each is to check the equation's coefficients. An equation with non-integer coefficients likely means that you have to use the formula. Still, even if the coefficients are all integers, completing the square may not work. Another rule of thumb is to calculate the discriminant (b^2-4ac). If that number is irrational (e.g. root 5), you won't easily solve it with the square completion method. There, you'll have to use the formula. In general, the formula method is more reliable and most of the times quicker than the other.

IP
Answered by Ioannis P. Maths tutor

3673 Views

See similar Maths A Level tutors

Related Maths A Level answers

All answers ▸

Write down the vector equation of the line l through the point (1,-1,2) and parallel to the vector 2i + 4k


How can I try and solve this differentiation, I don`t understand it?


Find the gradient at the point (0, ln 2) on the curve with equation e^2y = 5 − e^−x . [4]


What is differentiation and what can it tell me?


We're here to help

contact us iconContact ustelephone icon+44 (0) 203 773 6020
Facebook logoInstagram logoLinkedIn logo

© MyTutorWeb Ltd 2013–2025

Terms & Conditions|Privacy Policy
Cookie Preferences