MYTUTOR SUBJECT ANSWERS

352 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...

8 months ago

Answered by William, a GCSE Maths tutor with MyTutor


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

514 SUBJECT SPECIALISTS

£24 /hr

Lorna P.

Degree: Veterinary Science (Bachelors) - Bristol University

Subjects offered:Maths, Chemistry+ 1 more

Maths
Chemistry
Biology

“Hello!  A bit about me.. I'm currently studying Veterinary Science at the University of Bristol, having previously completed a degree in Zoology at the University of Leeds. I'm a patient person and think teaching others is a very rew...”

£18 /hr

Karishma D.

Degree: Medicine (Bachelors) - Imperial College London University

Subjects offered:Maths, Chemistry+ 3 more

Maths
Chemistry
Biology
-Personal Statements-
-Medical School Preparation-

“Hi guys, I'm a first year medical student at Imperial College London. I chose this degree because it indulges my passion for science whilst allowing me to interact with people, putting what I learn in the lecture theatre into practise...”

£18 /hr

Chris B.

Degree: Economics (Bachelors) - Durham University

Subjects offered:Maths, Further Mathematics + 2 more

Maths
Further Mathematics
Economics
-Personal Statements-

“About me: I am currently in my first year of studying Economics at Durham University. I have been tutoring maths for about two years now, so have had plenty of experience passing on my knowledge and interest in my subjects to younger ...”

MyTutor guarantee

About the author

William S. 11 Plus Maths tutor, A Level Maths tutor, 13 plus  Maths t...
£18 /hr

William S.

Degree: Medicine (Other) - St. Andrews University

Subjects offered:Maths, Physics+ 2 more

Maths
Physics
Further Mathematics
Chemistry

“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 can I solve simultaneous equations?

A right-angled triangle has base 10cm and height 4cm. What is the area of the triangle?

How do I simplify fully (p^3 x p^4)/p^2?

View GCSE Maths tutors

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

mtw:mercury1:status:ok