Solve x^2 + 8x +3 = 0 by completing the square.

Using the completing the square method:

1. Notice (x+4)2 = x2 + 8x +16 which differs from the question by a constant

2. So we can write: 

x2 + 8x + 3 = (x+4)2 - 13      (check this yourself if you don't see it immediately)

3. So from the question we get:

(x+4)-13 = 0

(x+4)= 13     (by adding 13)

x+4 = +-sqrt(13)    (square root remembering to include the +-)

x = -4 +-sqrt(13)      (subtracting 4)

So we have answers of:

x = - 4 + sqrt(13)

x = - 4 - sqrt(13)

which can both be checked by substitution into the original equation.

Answered by Tutor21349 D. Maths tutor

19960 Views

See similar Maths A Level tutors

Related Maths A Level answers

All answers ▸

When you integrate a function why do you add a constant?


What are the necessary conditions for a random variable to have a binomial distribution?


How would I use implicit differentiation to differentiate functions such as: y=tan^-1(ax^2+b) in the form of dy/dx=.....?


The Curve C has equation y = 3x^4 - 8x^3 -3. Find the first and second derivative w.r.t x and verify that y has a stationary point when x = 2. Determine the nature of this stationary point, giving a reason for your answer.


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