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

20124 Views

See similar Maths A Level tutors

Related Maths A Level answers

All answers ▸

How do changes to the coefficient of x affect the graph y = f(x) as opposed to changes to the coefficient of f(x)?


Statistics: Dave throws a ball at a bucket. The probability the ball goes into the bucket is 0.4. Dave throws the ball four times. What is the probability that he gets it in twice?


Find the first three terms in the binomial expansion of (8-9x)^(2/3) in ascending powers of x


Find the derivative of y=arcsinx


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