Why is completing the square useful and how do you do it?

Completing the square is nice and easy. If you have an equasion of the form x2+ax+b=0 then simply rewrite the equasion in the form (x+a/2)2-(a/2)2 +b=0. This may sound complicated but is we use numbers it becomes alot more simple, for example x2+6x+5=0 will then change to (x+3)2-9+5=ywhich then simplifies to (x+3)2-4=y
This is useful since it is quick to do and easy to see the interceptions with the axis. To find out when it cross's ' y' axis just sub in x=0 . In the previous example that would be (0+3)2-4=y and so 'y' would equal 5. Then to find out where it crosses the 'x' axis you make y=0 and solve for x. So in the earlier example (x+3)2-4=0 would then go to (x+3)2=4 then x+3=+-2 and so 'x' would equal 5 or 1. This very quickly allows us to make a quick sketch of the graph with thekey features.

EB
Answered by Edward B. Maths tutor

3191 Views

See similar Maths GCSE tutors

Related Maths GCSE answers

All answers ▸

2x + y = 1, x^2 + y^2 = 1


Factorise the expression: 2x^2 + 17x + 21


How to find the roots of a Quadratic Equation by Factorising?


Find the equation of the tangent to y = 2x^2 + 7 at x = 3.


We're here to help

contact us iconContact usWhatsapp logoMessage us on Whatsapptelephone icon+44 (0) 203 773 6020
Facebook logoInstagram logoLinkedIn logo

© MyTutorWeb Ltd 2013–2025

Terms & Conditions|Privacy Policy
Cookie Preferences