# Do you remember the formulas for

• razored
In summary, the conversation discusses the issue of forgetting mathematical formulas after a period of time, and various strategies for coping with this problem. Some suggest understanding the derivation of formulas, while others recommend regular practice and occasional use to keep them fresh in memory. Ultimately, it is agreed that understanding the concepts behind the formulas is more important than memorization, as reference books and notes can always be used during tests.
razored
Just curious, often in math I am presented with formulas and I always study them the day before the test; however, two weeks later, I cannot recall one formula. Am I the only one that does this? If so, I better be off and start learning them(I plan to). For instance, formulas like the finite arithmetic sum of a sequence. Even some simple formulas like that.

How do you cope with formulas?

Personally, I try and memorise as little as possible, since formulae can always be looked up in textbooks. For tests I did like you, try and memorise the ones that can't be derived easily, and then forgot them after a while. However, if one uses a formula a lot, then it will inevitably become imprinted in your mind. For example, most first year maths students know and can recite things like the quadratic formula (although, from my experience, there are some who can't!).

razored said:
Just curious, often in math I am presented with formulas and I always study them the day before the test; however, two weeks later, I cannot recall one formula. Am I the only one that does this? If so, I better be off and start learning them(I plan to). For instance, formulas like the finite arithmetic sum of a sequence. Even some simple formulas like that.

How do you cope with formulas?

One way for the long run is to understand how the formulas are derived. Then if you don't remember, you can go through the derivation. Things like the quadratic solution, sum of an arithmetic series, or sum of a geometric series are good examples where this would work.

I was never taught how the sum of an arithmetic series or geometric could be derived. Hm..

As cristo stated, the memorization will come with use. So if you are in a class that uses certain formulas often, it is natural that you will memorize them for some time, then when the class is over, and you don't use them as often they will slip your mind.

I would definitely try to understand the formulas you are using, but I think the memorization isn't as important as understanding, as there are plenty of reference books that house all types of formulas. As you advance try and pay closer attention to the theorems, definitions and proofs.

razored said:
I was never taught how the sum of an arithmetic series or geometric could be derived. Hm..

A(n):=d+2d+3d+4d+...+nd
A(n)=(1/2)(A(n)+A(n))
=(1/2)((d+2d+...+nd)+(nd+(n-1)d+...+d))
=(1/2)((d+nd)+(2d+(n-1)d)+...+(nd+d))
=(1/2)(n(n+1)d)
=d*n(n+1)/2

G(n)=1+r+...+r^(n-1)+r^n
rG(n)-G(n)=(r+r^2+...+r^n+r^(n+1))-(1+r+...+r^(n-1)+r^n)
(r-1)G(n)=r^(n+1)-1
G(n)=(r^(n+1)-1)/(r-1)

well, don't try to memorize them one day before a test. Do a couple of problems each day that uses each formula. Do this for a week or two and you will keep it with you. Even afterwards, use them everynow and then so you don't forget.

Take the IB exam, and you get Information Booklets which include most of the formulae that you need.

What I personally do is just work out the bare bones, then derive them if needed during the actual test. Saves lots of time for more practice.

get a note book and pencil and write down each different formula, and refer back when you need it.

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