MYTUTOR SUBJECT ANSWERS

240 views

How do I solve x^2+6x+8=0?

Ok, so we would call this a quadratic equation because it is written in the form of ax^2+bx+c=0 (in our case, a=1, b=6, c=8).

Luckily, this type of quadratic equation can be factorised, so we can solve it easily!

Ok, so we're trying to factorise x2+6x+8=0 so that it is in the form of (x+p)(x+q)=0.

Let's try expanding (x+p)(x+q)=0.

If you multiply the brackets together, you're left with:

x2+px+qx+pq=0

We can tidy this up a little bit to give us:

x2+(p+q)x+pq=0

This looks very similar to x2+6x+8=0, doesn't it?

Yes, it does! If we compare these two equations, we find out two things:

p+q=6

pq=8

So we're looking for two numbers which when they are multiplied by each other will give 8, and when they are added together will give 6. 

What we're left with is that p=4 and q=2 (or the other way round, it doesn't really matter).

Let's plug this back into our original equation: (x+p)(x+q)=0

Of course, now we have:

(x+4)(x+2)=0

This is much easier to solve than what we started with!

So in this case, either the first bracket is equal to 0 or the second bracket is equal to zero - this gives us two solutions for x.

Either x+4=0, meaning that x=-4

Or x+2=0, meaning that x=-2

So now we have the answers x=-2 or x=-4

Of course a quicker way to do this would be to look at x2+6x+8=0 and to find two numbers that are factors of 8 (they multiply together to make 8) and also add together to make 6.

William S. 11 Plus Maths tutor, A Level Maths tutor, 13 plus  Maths t...

6 months ago

Answered by William, a GCSE Maths tutor with MyTutor


Still stuck? Get one-to-one help from a personally interviewed subject specialist

330 SUBJECT SPECIALISTS

£18 /hr

Tamara T.

Degree: Philosophy (Bachelors) - Warwick University

Subjects offered: Maths, Geography+ 2 more

Maths
Geography
Further Mathematics
Economics

“I am a philosophy with economics student at the University of Warwick. I have always had a passion for numbers and thinking differently and hope this translates to you. I consider myself to be very friendly yet calm and patient. I hav...”

MyTutor guarantee

£20 /hr

Shivali J.

Degree: Medicine (Bachelors) - Imperial College London University

Subjects offered: Maths, Chemistry+ 5 more

Maths
Chemistry
Biology
.UKCAT.
.BMAT (BioMedical Admissions)
-Personal Statements-
-Medical School Preparation-

“Who am I? I am a first year medical student at Imperial College London. I have always been curious about the world we live in and have satisified this innate drive to understand the world around us through science. I hope to share thi...”

£20 /hr

Cesar Manuel F.

Degree: BSc Computer Science (Bachelors) - University College London University

Subjects offered: Maths, Physics+ 2 more

Maths
Physics
History
Computing

“Hello! My name is Cesar, I am originally from Perú but I currently study BSc Computer Science at University College London. I graduated Markham College with Distinction after completing my International Baccalaureate (IB) course, in w...”

About the author

£18 /hr

William S.

Degree: Medicine (Other) - St. Andrews Unversity University

Subjects offered: Maths, Physics+ 1 more

Maths
Physics
Further Mathematics

“I am a medical student at the university of St Andrews. I have always loved maths and sciences, and hope to share that passion with you too! I am patient and very friendly, so hopefully you will enjoy our sessions. Of course, you will...”

You may also like...

Posts by William

How can I find out the Young's modulus of a material?

How do I solve x^2+6x+8=0?

Solve the simultaneous equations 5x + 3y = 24 and 3x - 4y = 26

Other GCSE Maths questions

How to solve the simultaneous equations 3x+2y=7 and 5x+y=14

Make y the subject of (y/x)+(2y/(x+4))=3

Q: How to solve the simultaneous equations 3x+2y=7 and 5x+y=14

if x^2 + 9x + 20 = 0, what are the possible values of x?

View GCSE Maths tutors

Cookies:

We use cookies to improve our service. By continuing to use this website, we'll assume that you're OK with this. Dismiss

mtw:mercury1:status:ok