Math Is Fun Forum

BlitzBall

Member

Registered: 2012-01-07

Posts: 92

What is x^2+4x=12 ??

This is the part where I got stuck on...

x^2+4x=12
x^2+4x-12
(x+6)(x-2)   or    (x-6)(x+2)

Which one is right? And why? I'm leaning towards +6 and -2 because it meets 4x. But others say its -6 and +2
Also, is it okay if you can explain it simpler? Because I have got a lot of other topics that I am stuck on.
Thank you.

Last edited by BlitzBall (2012-01-07 16:14:23)

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: What is x^2+4x=12 ??

Hi BlitzBall;

Welcome to the forum.

You are right.

You can stop the argument my expanding.

(x+6)(x-2).

Have they taught you how? If not I will show you.

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

BlitzBall

Member

Registered: 2012-01-07

Posts: 92

Re: What is x^2+4x=12 ??

Hi BlitzBall;

Welcome to the forum.

You are right.

You can stop the argument my expanding.

(x+6)(x-2).

Have they taught you how?

Nope. Well, I'm at university and I have absolutely forgotten about algebra since Secondary school. I looked at the book and the answer is -6 and +2.

I will reply back to you tomorrow because its 4:17am

Thanks for your help:)

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: What is x^2+4x=12 ??

Hi BlitzBall;

x^2+4x=12
x^2+4x-12
(x+6)(x-2)   or    (x-6)(x+2)

Have you copied the problem correctly? Because if you did the book is wrong!

Which is not what you posted. The correct answer is

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

Bob

Administrator

Registered: 2010-06-20

Posts: 10,643

Re: What is x^2+4x=12 ??

hi BlitzBall and bobbym,

Welcome to the forum, BlitzBall.

Everyone (book included) is 'right'.

The difficulty lies here:

x^2+4x=12
x^2+4x-12
(x+6)(x-2)   or    (x-6)(x+2)

You started out with an equation and then lost the equals sign.

Here's the complete answer:

Don't forget the zero!

so

Now, if two factors multiply to make zero, one or the other must be zero.

so

Check these values.

Hope that wraps it up.

Bob

Last edited by Bob (2012-01-07 20:21:04)

---

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

BlitzBall

Member

Registered: 2012-01-07

Posts: 92

Re: What is x^2+4x=12 ??

hi BlitzBall and bobbym,

Welcome to the forum, BlitzBall.

Everyone (book included) is 'right'.

The difficulty lies here:

x^2+4x=12
x^2+4x-12
(x+6)(x-2)   or    (x-6)(x+2)

You started out with an equation and then lost the equals sign.

Here's the complete answer:

Don't forget the zero!

so

Now, if two factors multiply to make zero, one or the other must be zero.

so

Check these values.

Hope that wraps it up.

Bob

Hey bob, thanks for your reply. I think i got this because I looked at a website through BBC GCSE about Solving quadratic equations by factorising.

I think I understand this, I pick (x+6)(x-2) as it meets 12 and 4. Then I have to make it equal to zero. So, in the first bracket (x+6) i would have to subtract by -6 which makes zero! And same with the second bracket.   Is that the right way of how to do it??

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: What is x^2+4x=12 ??

Basically that is correct.

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

BlitzBall

Member

Registered: 2012-01-07

Posts: 92

Re: What is x^2+4x=12 ??

Basically that is correct.

YEAHHHHH!

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: What is x^2+4x=12 ??

Hi BlitzBall;

Do not forget to practice!

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

Bob

Administrator

Registered: 2010-06-20

Posts: 10,643

Re: What is x^2+4x=12 ??

Hi BlitzBall

FOOTNOTE:

a website through BBC GCSE about Solving quadratic equations by factorising

You could also try

http://www.mathsisfun.com/algebra/facto … atics.html

Bob

---

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob