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veterannz
02-11-2004, 01:18 PM
My daughter brought home some pre exam homework and after 40 years being away from school , I am unable to help her with the following sum.

Simplify the following

X2 + 8 X +15
------------------
X + 5

where I have written X2, I mean X squared. Apparently the answer is X + 3 but the only answer iI can get is X + 11. I hope there is someone out there who can show me how to get the correct answer

b1naryb0y
02-11-2004, 01:38 PM
1st clue:

What is 15 divided by 5?

veterannz
02-11-2004, 01:57 PM
I realise that I'm doing it wrongly but......... If I divide thru by X i get

X + 8 + 15
-------------
5

if i divide those numbers which are divisible top and bottom by 5 I get

X + 8 + 3.

So what am I doing wrong????
If I do as you suggest and just simplify the 15 and 5, what do you suggest I do with the *?

TonyF
02-11-2004, 01:58 PM
but the only answer iI can get is X + 11

Although x + 3 is the answer, the learning thing is to clarify how you arrived at x + 11.

veterannz
02-11-2004, 01:58 PM
oooops * should have read 8

~~~~~ s y ~~~~~
02-11-2004, 02:03 PM

Let's just proof that (x+5) (x+3) is the correct answer

(x+5) (x+3)
= (x*x)+(x*3)+(5*x)+(5*3)
=x^2+3x+5x+15
=x^2+8x+15

There you go. Simple. How can you get x+11?
(x+5) (x+11)
=x^2+16x+55 !!!

I'm a little suprised that although it's being 40 years since you left school, that you don't know this. Please don't remind me of the failing literacy and numeracy standards ... :(

Sorry, I don't know how you get the correct answer in step by step ways of doing things. I guess it would just be trial and error. But I can clearly see the answer just looking at it. Maybe it's just that I've done a million of these...

The only way I could think of is when you see a x^2 followed by something x and a number is to (x +/- ?) (x+/-?).. then take the number and find the factors of it. See if using these two numbers, you can somehow add or subtract to get the middle number.

I'm not sure if you can understand that, but it's probably the best I can do.

veterannz
02-11-2004, 02:14 PM
My daughter is 13.
I'm surprised that you are amazed at my lack of numeracy and literacy. I have not done algebra since 1955 and I was pleased that I still had a slight understanding of the problem. Whilst my literacy and numeracy are not up to your standards, at least my tolerance for those who dont have your supernatural talents must surely exceed yours. I only wanted a simple answer so I could help my daughter, not an example of the arrogance of the few !!
I presume you are not a teacher as your solution is not aimed at lesser beings such as myself..

veterannz
02-11-2004, 02:16 PM
by the way the answer supplied by the NZQA is X + 3 not (x+5) (x+3)

~~~~~ s y ~~~~~
02-11-2004, 02:18 PM
Sorry, but I did not mean any offence. There was nothing in your post or mine that suggested you had literacy standards of any sort, I'm just generalising. And no, I'm not a teacher...

Maybe I should stop helping people with Maths problems on this forum... I've taken all the effort to type out step by step, yet, you come and teach me about my lack of tolerance.

~~~~~ s y ~~~~~
02-11-2004, 02:20 PM
yes ok, well,

If (x+5) times (x+3) = x^2+8x+15

Then x^2+8x+15 divided by x+5 will be x+3

Just like 2*6=12
So 12/2=6

Spartacus
02-11-2004, 02:30 PM
The first step is to simplify the quadratic in the top line (numerator):

The coefficient of X2 (the number in front of the X2) is 1, which means we can try doing it the simple way: find two numbers that add to give the constant term (that is the 15), and multiply to give the coefficient of the X term (that is the 8). ie: 2 numbers that multiply to give 15 and add to give 8.

+5 and +3 spring to mind.

Thus we can simplify the numerator to

(X+5).(X+3)

The '.' means 'multiplied by'

Because we have an (X+5) in the numerator and the denominator (the bottom of the fraction), we can cancel them out. That's because we can re-write the fraction as:

(X+5) + (X+3) = (X+3)
------
(X+5)

hope this helps,
darren

Spartacus
02-11-2004, 03:08 PM
> (X+5) + (X+3) = (X+3)
> ------
> (X+5)

Sorry that should be

(X+5) * (X+3) = (X+3)
------
(X+5)

andrew93
02-11-2004, 03:42 PM
X2 + 8 X +15
--------------------
X + 5

=

(X + 5) * (X + 3)
--------------------
(X + 5)

=

(X + 3)

=

X + 3

45South
02-11-2004, 03:43 PM
Bloody hell, how's that lot gonna help you work out if the shopkeeper gave you the right change for a loaf of bread.

Spartacus
02-11-2004, 04:12 PM
> if the shopkeeper gave you the right change for a

Change for bread was Form 1 - this'll let you know whether the structural supports of the shopkeeper's shelves will sufficiently support the weight of the bread

;) darren

45South
02-11-2004, 04:17 PM
>Change for bread was Form 1 - this'll let you know whether the structural supports of the shopkeeper's shelves will sufficiently support the weight of the bread

lol

veterannz
02-11-2004, 04:39 PM
LOL
many thanks to all the contributors. My daughter was able to relate the information supplied to a previous school lesson. Phew

MartynC
02-11-2004, 04:45 PM
I wonder how i ever got thru Form 5, 6 or 7, or even Uni Stage 1 Calc or Stats :(

MrBeef
02-11-2004, 06:27 PM
sy u seem to be a math illeterate (sp?)

I dont know if you've seen last years level 2 90284. But for anyone else heres a question.

Please not im doing level 2 maths..so i only saw this first today, but I got it.

___________

tara has a rectangular lawn that is 11 m long and 8 m wide.
The lawn is to be surrounded by a path.
The width of the path on each side of the lawn is the same.
The path has an area of 100m^2>

Calculate the width of the path.
_____________________
| ______________ |
| | | |
| | | |
| | | |
| | | |
| |_____________ | |
|____________________|

Thats the idea..sorry about poorly drawn...

But yeh calculate the width of the path around the lawn.

MrBeef
02-11-2004, 06:29 PM
ok, that drawing completely f**ked up

~~~~~ s y ~~~~~
02-11-2004, 06:51 PM
Roughly 2.15m is it? Can't be bothered getting a calculator...

This sounds roughly like a Merit question

MrBeef
02-11-2004, 06:54 PM
you've obviously seen the question before.

but yes, 2.15 roughly.

~~~~~ s y ~~~~~
02-11-2004, 07:50 PM
> you've obviously seen the question before.
>
> but yes, 2.15 roughly.

No I haven't actually..... I have just found the exam paper at close to the bottom of the school bag. We got given heaps to do during our study leave, which started two weeks ago, but I haven't touched it yet as the exams aren't till 23rd Nov anyway.