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#128 Re: Help Me ! » Simplify » 2006-01-06 11:19:11

appologise, grassy homes.

#129 Re: Help Me ! » Simplify » 2006-01-06 10:41:02

Sounds like a job for Crazy Holmes wink

#130 Re: Help Me ! » Differentiation » 2006-01-06 10:10:22

I'm a little stuck again:
find the gradiaent of the tangent and the normal to the following curves at the stated point.

y = x + 1/x  at x = 1/2.

dy/dx = -x^-2 + 1  = 3/4,  thus the gradient of the normal is -4/3.

I can work out most of these sums, I am doing somthing wrong with the negative power...

#131 Re: Help Me ! » Simplify » 2006-01-06 10:06:12

I'd start with x/x^2, firstly I'd "reciprocal" which basically means you take the value with the power (x^2) and move it to the top, when you do this you MUST change the sign of the power:

x / x^2  = x * x^-2

I'd then do the same with the next part of the sum, giving you b - ax * x^-3.  Now all that is left is

(x * x^-2) + (b - ax * x^-3), since none of the values share similar powers, I think this is as far as you can go.  (Don't take my word for it, I'm new to this too).

#132 Re: Help Me ! » Simplify » 2006-01-06 09:36:37

Thankyou, I was drunk sad
Won't happen again.

#133 Re: Jokes » joke about pi » 2006-01-05 19:58:08

maybe you'll have heard of the expression "pwned" which is derived from the word "owned".  I recently read a question asking how this word was to be pronounced, many people had many thories.  My theory is that since it is internet slag, the word was not meant to be pronounced (only typed) and thus the internet is spawning a global language that has no pronounciation.  Do any other languages such as this exist?

#134 Re: Jokes » Why is six afraid of seven? » 2006-01-05 19:50:44

Maybe 6 was in a bar and heard some really bad things about 7.

#135 Help Me ! » Simplify » 2006-01-05 19:35:33

RickyOswaldIOW
Replies: 17

x(x-1)(x+1)
do I multiply the brackets by eachother first, or each bracket by x?

#136 Re: Help Me ! » Rounding .5 up or down? » 2006-01-05 18:23:53

Consider this: you have a bag of sweets containing 10 whole sweets but lots of shrapnel in the bottom of the bag.  The shrapnel could make up 3/4 of a sweet yet you'd still say you have 10 sweets.  Then in this case, are you not rounding down even though you have more than .5?  I don't think you can "prove" which way to round, people just do it to simplify a number, it's not actually a mathematical theory (or somthing).

#137 Re: Help Me ! » Differentiation » 2006-01-04 16:20:49

Thanks again, one final question, the only one left that I am unsure of my workings:

y = sqrt(4/x^3) = sqrt(4x^-3) = 2x^-3/2
dy/dx = -3x^-5/2
Is this right?

#138 Re: Help Me ! » Rounding .5 up or down? » 2006-01-04 15:40:59

I think people like to round up becuase the most public use of rounding is related to money handling.  rounding up = more $$$.

#139 Re: Help Me ! » Differentiation » 2006-01-04 15:34:37

in a question like y = 3x^4,  do you multiply the 4 by the 3 to make dy/dx = 12x^3?
i.e.  y=ax^b   dy/dx = (ba)x^b-1

#140 Re: Help Me ! » Differentiation » 2006-01-04 15:30:40

I was subtracting 1... but from +4 and not -4 tongue
Thanks.

#141 Help Me ! » Differentiation » 2006-01-04 14:42:19

RickyOswaldIOW
Replies: 13

Hi guys and girls, long time no see.  I've been away for the Christmas holidays (away from my computer at least) but now I am back to bug you with more laughably simple questions!

I've moved on to the topic of calculus and am having a little trouble with some differentiation questions.  I understand how to do basic questions such as y=x^10   dy/dx = 10x^9.
I think these are also correct, only my book shows the answers in a different format, I'd be obliged if you could check.

y = 1/x = x^-1    dy/dx = -x^-2    (book says: -1/x^2)

y=sqrt x = x^1/2    dy/dx = 1/2x^-1/2    (book says: 1/ 2sqrt x)

y= -1/x^4 = -x^-4  dy/dx = 4x^-3      (book says: 4/x^5)


P.S. Happy New Year!

#142 Re: Help Me ! » Factorising quadratics... again » 2005-12-17 08:06:37

I'm still having a little trouble with this.

y = ax^2 + bx + c
and our answer needs to be in the format
(dx + e)(fx + g)  where:

e * g = a * c
and
e + g = b

in a question like y = -x^2 + 3 + 4 I would take the negative co-efficient from x^2 and reverse the other signs, factorise and then put the - back in front of d making d * f = a??

If I have a question like y = -2x^2 - 3x + 2
I'll change it to -(2x^2 + 3x - 2)
like this I can see that  e = 4, g = -1, d = 2 and f = 1.
This is where I go wrong, into my answer I would now write
-[(2x + 4)(x - 1)]
Which of cours, is wrong.   Do I need to divide e by d?

#143 Re: Help Me ! » Factorising quadratics... again » 2005-12-17 07:55:42

The picture of yours that I see has the hat on! Are you trying to change it back to your normal one?

#144 Re: Help Me ! » Factorising quadratics... again » 2005-12-17 07:36:01

Merry  Christmas  Krassi  and  Mathsy smile

#145 Re: Help Me ! » Factorising quadratics... again » 2005-12-17 07:06:57

so you're saying I should divide the whole equation through by the co-efficient of x^2 and then factorise normally, multiplying the co-efficient back in at the end?

#146 Help Me ! » Factorising quadratics... again » 2005-12-17 06:52:07

RickyOswaldIOW
Replies: 17

I have problems when trying to factorise a quadratic where the co-efficient of x^2 is < -1  i.e.

y = -2x^2 - 3x + 2

What are the steps I need to take to get an answer in the form (ax + b)(cx + d)?

#147 Re: Help Me ! » i find maths impossible,literally » 2005-12-17 06:33:47

Learning maths for the sake of learning maths is probably very dull.  Most people learn maths because they need to for somthing else i.e. software development.
   I've found studying maths can be a little tedious, but I only fail at learning it if I try to understand the maths from the start.  When I am being taught a new method in mathematics, instead of trying to UNDERSTAND what is going on, I just accept the steps I need to take and take them.  The understanding of what's happening usually sinks in when you have been working with somthing for a while.

#148 Re: Help Me ! » Solving a Cubic equation » 2005-12-05 04:07:00

4x - 3x = CUBE ROOT OF 1/2?

I thought I knew how to do this, but maybe not.

#149 Re: Help Me ! » Solving a Cubic equation » 2005-12-05 04:04:32

To solve the equation you just have to remember that whatever you do to one side you must do to the other.  The idea is to get the x on it's own.

so 4x^3 - 3x = 1/2 becomes
    4x^3 = 3x + 1/2

You see that I made the "-3x" on the left equal 0 by adding 3x to it.  Because I added 3x on one side I must add 3x onto the other side too.
   For the next step you must take that 4 off from in front of the x^3  (that 4 means multiply so you must divide 4x^3 by 4 to get it as x^3).  Again, since you have divided 4 on one side, so you must on the other.

x^3 = (3x + 1/2)  / 4

   Finally, the opposite of "cubing" a number (which is what the ^3 does) is finding it's cube root.  so x = CUBE ROOT OF (3x+1/2)/4
          -2x = CUBE ROOT OF 1/8
   You'll probably need a calculator for that last step smile

#150 Re: Help Me ! » Perpendicular line equations. » 2005-12-05 03:52:09

The perpendicular line would be:
y = 3/2 x + 1
2y = 3x + 2

Thanks irspow but you're a bit late tongue

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