Need this formula re-arranged

[si_the_geek]

Hi folks, it's not like me to post questions, but here we go....

I've got this formula:

T = N * (B + [(N-1) * E]/2 )

Unfortunately the variable I want to calculate is N, and no matter what I do I can't seem to get N on it's own

How should it be?

N = ????

[Lightning]

Askthis in the math forum ,they might solve it within 5 min or so.

[Bazzlad]

is E the exponential function?

[DiGiTaIErRoR]

n=+/- (sqr(8*e*t+(2*b-e)^2) - 2*b +e) / 2*e

[agmorgan]

I think that comes from rearranging the formula to
0= n^2E +n(2B-E) -2T
then solving the quadratic equation.
Am I right?

I used to be able to do these, now Ive turned a bit thick from lack of practice

[si_the_geek]

Originally posted by DiGiTaIErRoR
n=+/- (sqr(8*e*t+(2*b-e)^2) - 2*b +e) / 2*e

perfect!!

I've got no idea how you found it, but it returns the right answer for all my test cases.

Thanks DiGiTaIErRoR

[agmorgan]

Originally posted by si_the_geek
perfect!!

I've got no idea how you found it, but it returns the right answer for all my test cases.

T = N * (B + [(N-1) * E]/2 )
T = NB + N * ([(N-1) * E]/2 )
T = NB + [(N ^2 - N) * E] /2 
2T = 2NB + (N ^2 - N) * E
2T = 2NB + N ^2 * E - NE
0 = EN ^2 + (2B-E)N - 2T
0 = ax^2  +  bx     + c
 
x = [-b +- SQR(b^2 - 4ac)] /2a
 
Therefore
N = [-(2B-E) +- SQR([2B-E]^2 - 8ET)] /2E

[si_the_geek]

Originally posted by DiGiTaIErRoR
I'm positive:

n=(2*t/n-2*b)/e+1

is also correct.

True, but it also doesn't have N on it's own

This isn't something that needs to run fast, so the first answer you posted is certainly good enough!

Thanks again

[DiGiTaIErRoR]

Originally posted by si_the_geek
True, but it also doesn't have N on it's own

This isn't something that needs to run fast, so the first answer you posted is certainly good enough!

Thanks again

I should get more sleep.