2 math problems

[CODE-D]

Hello If you dont know me all you need to know is that Im smart except when it comes to math, its like kryptonite to my brain and I shut down(but Im getting better)

but I just need some reassurance on these 2 problems I solved
#1 using the quadratic formula
3x^2 - x = 0


and
#2
1 over 5x + 20 minus 3 over x^2 - 16 = 1 over x-4

Im confused on this one when it comes to the common denominator for the first term especially.

 

[SckizoBoy]

1. x = 0 or 1/3

(factorises to 'x(3x-1) = 0') *shrug* not much more to it...

2. 1/(5x+20) - 3/(x[sup]2[/sup]-16) = 1/(x-4)

(could've written that a little more clearly... sorry, pet peeve)

Anyway, factorise the denominator of the second expression, and you get as follows:

1/(5x+20) - 3/(x-4)(x+4) = 1/(x-4)

Add the highlighted bit to both sides:

1/(5x+20) = 3/(x-4)(x+4) + 1/(x-4)

Multiply both top and bottom of the highlighted section by '(x+4)':

1/(5x+20) = 3/(x-4)(x+4) + (x+4)/(x-4)(x+4)

Resolve:

1/(5x+20) = (x+7)/(x-4)(x+4)

Cross multiply (i.e. multiply both sides by (x-4)(x+4)(5x+20)

(x-4)(x+4) = (x+7)(5x+20)

x[sup]2[/sup]-16 = 5x[sup]2[/sup]+55x+140

Resolve to left hand side = 0

0 = 4x[sup]2[/sup]+55x+156

Whack into the quadratic formula

[(-55 (+/-) 529[sup]1/2[/sup])/2]

' *shrug*

Well, something along those lines...

 

[DoPo]

1. x = 0 or 1/3

(factorises to 'x(3x-1) = 0') *shrug* not much more to it...

What he said, I'll just elaborate a bit.

When you have this

x(3x-1) = 0

it becomes immediately obvious that one of the solutions is zero (because zero times whatever equals zero). Now you only have to find out

3x - 1 = 0

which is 1/3. That's why the answers are 0 and 1/3.

I'll double check the calculations for the second problem (I didn't look at them yet) but I feel they would be correct.

EDIT: I'm looking at it now. Something seems wrong. why didn't you factorise (5x+20) into 5(x+4)? I'm probably missing something. Let me take a better look (also I woke up quite early this morning so I'm tired now).

EDIT 2: Fuck, I can't Math. I just got x=(-31/6) for the second one. I don't think that's right - it's too easy. I'll go back through my calculations.

 

[DoPo]

I must be doing something wrong. I can't see it. Here's what I have and I'm struggling to see the error:

Start off with this:
1/(5x+20) - 3/(x2-16) = 1/(x-4)

Factorise the denominators
1/5(x+4) - 3/(x-4)(x+4) = 1/(x-4)

Note down somewhere that x =/= +/-4 because you'll have division by zero then.

Move the right side to the right side:
1/5(x+4) - 3/(x-4)(x+4) - 1/(x-4) = 0

Do the thing which I don't know how it's called but multiply each fraction to make the denominators even. And they should be all even to 5(x+4)(x-4). Also I'll discard the denominator for this to make writing the thing easier:

[(x-4)*1] - (3*5) - [1*5(x+4)] = 0

And you get

x - 4 - 15 - 5x - 20 = 0

Which comes down to

-5x - 31 = 0

Then

5x = -31

And finally

x=(-31/5)

WHAT IS WRONG HERE?! It shouldn't be that easy, right?

EDIT: I swapped italics for bold to make it stand out more.

 

[Brandon237]

Okay, the first one is easy and has already been answered...
As for the second one: PLEASE put that down a lot more clearly, I cannot tell where one term ends and the next starts. Brackets are your friend.

I get the totally screwed answer of X = (-39/4)
When using the calculator to solve, I get that the whole rearranged equation equals 0.0298, and it was being squared, so... close enough -39/4 works, I guess.

To solve, you factorise and rearrange as:
*1/5(x + 4)* - *3/(x - 4)(x + 4)* - *1/(x - 4)* = 0

Then multiply out by an LCD of: 5(x + 4)(x - 4)

you will get to:
4x = -39

If you want me to add working out, just quote and ask.

 

[SckizoBoy]

EDIT: I'm looking at it now. Something seems wrong. why didn't you factorise (5x+20) into 5(x+4)? I'm probably missing something. Let me take a better look (also I woke up quite early this morning so I'm tired now).

Yeah... should've done that...

So, [user]brandon237[/user]'s got it... weird answer... -39/4, but it's right AFAICT (though to be fair, working it out in my head... which is a method that is failing more and more in my senility...(!))

 

[DoPo]

Okay, the first one is easy and has already been answered...
As for the second one: PLEASE put that down a lot more clearly, I cannot tell where one term ends and the next starts. Brackets are your friend.

I get the totally screwed answer of X = (-39/4)
When using the calculator to solve, I get that the whole rearranged equation equals 0.0298, and it was being squared, so... close enough -39/4 works, I guess.

To solve, you factorise and rearrange as:
*1/5(x + 4)* - *3/(x - 4)(x + 4)* - *1/(x - 4)* = 0

Then multiply out by an LCD of: 5(x + 4)(x - 4)

you will get to:
4x = -39

If you want me to add working out, just quote and ask.

Yes, you are correct. And I was on the right path but I see my mistake - I really can't math.

And you get

x - 4 - 15 - 5x - 20 = 0

Which comes down to

-5x - 31 = 0

No, it doesn't come down to that, you moron. Learn to fuckin' do basic algebra. It comes down to

-4x - 39 = 0

You somehow dropped x entirely and then added 4 rather than subtracting it. You are a disgrace!

P.S. When I did it on paper I still did two things wrong: I multiplied the first number by (x+4) rather than (x-4) and then when I did (x-5x) somehow that resulted in -6x. What the actual fuck is wrong with me? I'm tired but I shouldn't be that tired. Maybe I'll just go to bed early.

 

[Brandon237]

So, [user]brandon237[/user]'s got it... weird answer... -39/4, but it's right AFAICT (though to be fair, working it out in my head... which is a method that is failing more and more in my senility...(!))

Yes, you are correct. And I was on the right path but I see my mistake - I really can't math.

Yay, I was right ^.^

Someone should hit me right about now.
And lol DoPo, no need to be so hard on yourself

I wonder if this answer is maybe a little late for the OP though... oh well.

 

[DoPo]

I wonder if this answer is maybe a little late for the OP though... oh well.

It has only been a bit less than two hours since he posted it, so I hope not. Unless he was doing a test at that time, in which case the answer may be rather late. Also, he shouldn't have done it at a test because as you see it's easy to get a wrong response quickly.

[sub][sub][sub]And it's cheating.[/sub][/sub][/sub]

 

[SckizoBoy]

Someone should hit me right about now.

Gladly! I used to be good at maths, damnit! XD

 

[Brandon237]

I wonder if this answer is maybe a little late for the OP though... oh well.

It has only been a bit less than two hours since he posted it, so I hope not. Unless he was doing a test at that time, in which case the answer may be rather late. Also, he shouldn't have done it at a test because as you see it's easy to get a wrong response quickly.

[sub][sub][sub]And it's cheating.[/sub][/sub][/sub]

To be blunt the Escapist is not the first place / person I would go to to cheat on a Maths test
And if he needs to know how to solve number 1 right now (then) in a test I think he is screwed already >.< Fine for classwork, but by the test-time you may want to know common factors...

[sub][sub][sub]You mean they STILL don't allow cheating these days? Jeesh, society is slow...[/sub][/sub][/sub]

Someone should hit me right about now.

Gladly! I used to be good at maths, damnit! XD

I am currently in Grade 11 / standard 9, so I did this in the last 2 months, So you do have an excuse I am also taking Advanced Programme Maths, so if I didn't get this, you could hit me even harder... for my own safety I may want to stay off these threads come to think of it >.<

 

[SckizoBoy]

I am currently in Grade 11 / standard 9, so I did this in the last 2 months, So you do have an excuse I am also taking Advanced Programme Maths, so if I didn't get this, you could hit me even harder... for my own safety I may want to stay off these threads come to think of it >.<

Good grief... a whippersnapper! =P

And in my defence, the last time I properly did stuff like this was... shit... seventeen years ago... fuck, I'm old! XD

[sub][sub][sub]And it's cheating.[/sub][/sub][/sub]

Not it's not, it's called 'maximisation of the utility of available resources'...(!)

 

[CODE-D]

My teacher allows help with homework and I got it now.

 

[Brandon237]

Good grief... a whippersnapper! =P

And in my defence, the last time I properly did stuff like this was... shit... seventeen years ago... fuck, I'm old! XD

Indeed I am
And no, I WON'T get off anyone's lawn!

Damn, I suppose if you don't use it this stuff disappears damn fast >.< Although I will likely (if I am able to find a position in anywhere in the sorts of fields I really want to work) go into a career where intense maths is a part of daily work, my children are gonna want to kill me...
[sub][sub][sub]It is not cruel to hold back supper until they can factorise cubic equations with complex roots![/sub][/sub][/sub]

My teacher allows help with homework and I got it now.

KK, glad to be of service ^.^

I really wish that the Escapist would stack quote/end quote tags instead of adding them directly to the next block of text and leaving me trying to find the formatting in a torrent of text. Surely they can insert a line-break before and after the quote formatting when you click quote.

 

[DoPo]

[sub][sub][sub]You mean they STILL don't allow cheating these days? Jeesh, society is slow...[/sub][/sub][/sub]

It's not allowed only technically. I mean you won't get into any trouble if you don't get caught. And those who do get caught just played their role. Students are getting better and better in cheating and worse and worse in actually knowing and understanding the material. Evolution!

I joke of course. But cheating is a time honoured tradition. It was thanks to that I managed to finish school. Literature really wasn't my thing. And there was the entire year 10 where I learned nothing at all from Biology - the teacher sucked that much that I sort of skipped Biology that year. I'm not joking either.

Not it's not, it's called 'maximisation of the utility of available resources'...(!)

OK, my school system really sucked - we didn't have that definition. Oh well, in that case I'm happy, apparently I maximised the utility of my literature and Biology.

I am currently in Grade 11 / standard 9, so I did this in the last 2 months, So you do have an excuse I am also taking Advanced Programme Maths, so if I didn't get this, you could hit me even harder... for my own safety I may want to stay off these threads come to think of it >.<

What would "standard 9" be?

I did those in...hmm let me think, I thing grades 10-11. Maybe 9-10. I'm not sure. I'm pretty sure it was around 10. We started quadratic equations in grade 8 and then it seems we had it ever since. I can still recite the formula in my sleep[footnote]The funny thing is we only had it at Uni twice - once in a Maths lecture we were told "well there is a formula for quadratic equations but if you need it look it up" and once last week we only mentioned it while discussing something completely unrelated to algebra.[/footnote]. And I finished school, erm, four years ago. I was also in a class that studied Maths more intensively than the rest of my school. We were on par with the fickin' Maths Hight School where they studied Maths more intensively than everybody else in the town.

 

[Brandon237]

What would "standard 9" be?

I did those in...hmm let me think, I thing grades 10-11. Maybe 9-10. I'm not sure. I'm pretty sure it was around 10. We started quadratic equations in grade 8 and then it seems we had it ever since. I can still recite the formula in my sleep[footnote]The funny thing is we only had it at Uni twice - once in a Maths lecture we were told "well there is a formula for quadratic equations but if you need it look it up" and once last week we only mentioned it while discussing something completely unrelated to algebra.[/footnote]. And I finished school, erm, four years ago. I was also in a class that studied Maths more intensively than the rest of my school. We were on par with the fickin' Maths Hight School where they studied Maths more intensively than everybody else in the town.

Standard 9 is what my parents call grade 11, older generation thing, but often helps for them to understand and not do the mental hoops

I take the AP maths as an extra subject, in school we get two "choices", 1 choice is normal maths if you want to not work as a manual labourer, and then "maths literacy" which counts jack-shite for university, teaches no higher-grade algebra, trigonometry, functions, anything like that and will get you either into working with your hands at a technikon, or working with your hands and a broom. It is not a good idea to take maths literacy. A 50% in Maths Normal is worth more than an 80% in maths Lit.

I MAY have gone off on a tangent[footnote]This thread (that pun included) alone could justify my execution under certain governments, I am sure of it [/footnote] there.

 

[TheYellowCellPhone]

Yeah, I can't read math when it's written like that.

But Imma drop this here.

http://www.wolframalpha.com/

 

[DoPo]

This thread alone could justify my execution under certain governments, I am sure of it

If you mean you badmouthing the school system, then: puh-leeeease. The best thing I can say about my school system, and my school, too,is not to speak at all. I didn't really like it, to say the least. My view is that it needs some reformation, namely to be burned to ashes and totally replaced. I once spoke with somebody else about it and they didn't appreciate me saying that, so I mostly don't mention it.

No wonder I study abroad now.

 

[SckizoBoy]

Indeed I am
And no, I WON'T get off anyone's lawn!

*shakes walking stick at* LOL... but I'm only twenty five!

I joke of course. But cheating is a time honoured tradition. It was thanks to that I managed to finish school. Literature really wasn't my thing. And there was the entire year 10 where I learned nothing at all from Biology - the teacher sucked that much that I sort of skipped Biology that year. I'm not joking either.

Yeah... for the most part, always gotta cheat a bit to get through high school... though biology was awesome for me. Had a tubby little Scot teach us that for GCSE (grade 10/11, I think) and he brought up drugs chemistry/biology and taught us the start of a phonetic guide to the spinal nerve connections of C1-6: Oh oh oh... to touch and kiss... (for occipital, omohyoid etc. etc.). Only, the next three were all 'v', so he never bothered to teach us the rest! *snrk*

 

[DrRockor]

OH GOD MY BRAIN! I happily forgot the majority of algebra after I left highschool. I can do the math that I need, thats it