Maths Difficulty.....Please Help Somebody :)

ZJuwelH

Massive round of applause for bhaal85 and theone! But theone, your method was well long and a headf**k, I'm just going to try to remember bhaal85's, sorry! If it's any consolation I might just ask my teacher...

No problem, both methods are a pain in the ass to be perfectly honest. The only way to get 'good' at using such methods is loads of practice....

Reply 64

Rich

2

clever_lad

"Complete The Square For the Following Quadratic, then state a value of x which gives the least/minimum value. quadratic: 3x^2 + 8x + 16"

i know how to complete the square, but i dont understand what the second part of the question is about...please help!!

Completing the square (I can't understand why anyone would need any special 'methods' to do such a simple procedure as this; just get the x^2 and x terms correct and then subtract whatever you need to to get the constant correct):


f(x) = 3x^2 + 8x + 16 = 3*(x + 4/3)^2 - 16/3 + 16 = 3*(x + 4/3)^2 + 32/3

Now, the smallest value which f(x) can take is clearly when 3*(x + 4/3)^2 is equal to zero. This is because 3*(x + 4/3)^2 cannot be any less than zero (a real number squared is always greater than or equal to zero) and the term 32/3 is constant. So we need to find x where x + 4/3 = 0, and by solving this simple linear equation, we see that the minimum occurs where x = -4/3.

Regards,

Reply 65

Rich

2

ZJuwelH

Massive round of applause for bhaal85 and theone! But theone, your method was well long and a headf**k, I'm just going to try to remember bhaal85's, sorry! If it's any consolation I might just ask my teacher...

The simplest way to remember how to complete the square (if you can't do it intuitively) is the simple identity:


ax^2 + bx + c = a*(x + b/(2a))^2 - b^2/(4a) + c

Regards,

Reply 66

rahaydenuk

The simplest way to remember how to complete the square (if you can't do it intuitively) is the simple identity:


ax^2 + bx + c = a*(x + b/(2a))^2 - b^2/(4a) + c

Regards,

No offence Hayden, but I doubt that amidst the large number of things that most people have to learn, and I'm not including those who can do this process 'intuitively', that they will be able to remember this long identity, but rather will need to know a method they can use.

And on a different note, I think your atheist quote is quite cool.

Reply 67

theone

No offence Hayden, but I doubt that amidst the large number of things that most people have to learn, and I'm not including those who can do this process 'intuitively', that they will be able to remember this long identity, but rather will need to know a method they can use.

And on a different note, I think your atheist quote is quite cool.

good quote.

Reply 68

Juwel

18

theone

No offence Hayden, but I doubt that amidst the large number of things that most people have to learn, and I'm not including those who can do this process 'intuitively', that they will be able to remember this long identity, but rather will need to know a method they can use.

And on a different note, I think your atheist quote is quite cool.

Oh I think I can manage to remember it bhaal! But what does it replace in my finite memory...
Doh sin x / cos x is what again? sec x? cos^2 x?

Reply 69

Rich

2

theone

No offence Hayden, but I doubt that amidst the large number of things that most people have to learn, and I'm not including those who can do this process 'intuitively', that they will be able to remember this long identity, but rather will need to know a method they can use.

And on a different note, I think your atheist quote is quite cool.

You call that a 'long identity'?! It's worrying enough that students of A-level maths feel the need to even use 'trained-monkey' identities and methods for simple processes like completing the square (this is mainly a problem of teaching style, not of ability of the students, may I point out), but when the above is considered too long an identity to remember, one really does start to despair. :rolleyes:

Thanks for the comment regarding the quote. :smile:

Reply 70

Unregistered

"Find The Minimum Value of the quadratic expression 3x^2 - 12x + 5 and state a value of 'x' which gives the minimum value."

hint. :first you are required to complete the square of the quadratic equation........

help please!!!!!!!!!

Reply 71

rahaydenuk

You call that a 'long identity'?! It's worrying enough that students of A-level maths feel the need to even use 'trained-monkey' identities and methods for simple processes like completing the square (this is mainly a problem of teaching style, not of ability of the students, may I point out), but when the above is considered too long an identity to remember, one really does start to despair. :rolleyes:

Thanks for the comment regarding the quote. :smile:

No probs.

My point is that there are so many identites to learn for the majority of students who do not intuitvely understand most of concepts and there's only so much that teaching can do, although I agree it's far below standard.

And I would consider that a 'long' identity. It is not something I coudl commit to memory and use confidently without looking up beforehand ,with spending a decent bit of time of learning it, and without any sort of logic. Think how many identites have to be learned for just one module of maths, the number could well approach or exceed 50 in the most common module, i.e. P1, P2, etc. and this is just one module of one subject, so I wouldn't expect students to commit this to memory, since most people won't remember it to be honest (and i speak from personal experience). Very few students, possibly myself included, have the intelligence to grasp and remember all A-Level identites.

Anyway, this is just my opinion.

Reply 72

Unregistered

i would really appreciate some help guys..... :smile:

Reply 73

rahaydenuk

You call that a 'long identity'?! It's worrying enough that students of A-level maths feel the need to even use 'trained-monkey' identities and methods for simple processes like completing the square (this is mainly a problem of teaching style, not of ability of the students, may I point out), but when the above is considered too long an identity to remember, one really does start to despair. :rolleyes:

Thanks for the comment regarding the quote. :smile:

I personally, could remeber that forumal, I would be willing to learn forumlas, as I tend never to use the forumla booklet. But for students who have just done their GCSEs its a lot to ask off them, considering the step up to A Level. There are the few who can cope with it, then there are the ones who winge and complain every waking moment.

Reply 74

Unregistered

i would really appreciate some help guys..... :smile:

How about checking the other massive thread on completing the square?

Reply 75

Unregistered

nooooooooo.......too much info.please could you help me on this one.... :smile:

Reply 76

theone

How about checking the other massive thread on completing the square?

Good thinking......................

*shows his typing fingers*

Reply 77