cosine without pi

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39 comments, last by cplusasterisk 21 years, 6 months ago
Your equation is blatantly wrong - ln(a) (a E |R) isn''t defined for a <= 0.
The Euler angle formula is e^(i*phi) = cos(phi) + i * sin(phi).
E8 17 00 42 CE DC D2 DC E4 EA C4 40 CA DA C2 D8 CC 40 CA D0 E8 40E0 CA CA 96 5B B0 16 50 D7 D4 02 B2 02 86 E2 CD 21 58 48 79 F2 C3
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My favourite way of computing Pi is based on the curious fact that the probability of two random integers being relatively primes is P = 6/Pi^2 (I didn''t smoke anything weird). So you can just estimate that probability by generating a bunch of random integers and checking if they are relatively prime. The last step is Pi = sqrt(6/P).

quote:
Your equation is blatantly wrong - ln(a) (a E |R) isn''t defined for a <= 0.


Not exactly true. In complex analysis, log is a multi-valued function, and the possible values of ln(-1) are (2*k-1)*i*Pi, where k is an integer, so the formula is right if you select the appropriate branch of logarithm in that region.

Yep, I know.
Sorry, I thought you meant ln: |R -> |R. Gotta write -1 E C or (-1, 0), or I''ll go making false assumptions
E8 17 00 42 CE DC D2 DC E4 EA C4 40 CA DA C2 D8 CC 40 CA D0 E8 40E0 CA CA 96 5B B0 16 50 D7 D4 02 B2 02 86 E2 CD 21 58 48 79 F2 C3
quote:Original post by Jan Wassenberg
Sorry, I thought you meant ln: |R -> |R. Gotta write -1 E C or (-1, 0), or I''ll go making false assumptions

I thought the "i" make it quite clear what he meant...
pi is something like 4*(1/2 + 1/3 - 1/4 + 1/5 - 1/6 ...)

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Here's a few...

π = 22/7

π/2 = (2 × 2 × 4 × 4 × 6 × 6 × 8 × … ) / (1 × 3 × 3 × 5 × 5 × 7 × 7 × … )

π/4 = 1 - 1/3 + 1/5 - 1/7 + 1/9 - …

π/6 = 1/2 + 1 / 2(3 × 23) + (1 × 3) / (2 × 4)(5 × 25) + (1 × 3 × 5) / (2 × 4 × 6)(7 × 27) + …

π = 2√3 * (1 - (3 * 3)^-1 + (3^2 * 5)^-1 - (3^3 * 7)^-1 + … )

π^3 / 8 = ∫ (log x)2 / (1 + x2) dx from 0 to ∞

[edited by - Dracoliche on October 10, 2002 12:05:59 PM]
drac: sorry, but according to windows calculator 22/7 is out by 0.00126448926734961868021375957764
D''oh! I meant 355/113!
quote:
I don''t care what pi specificaly is, and I know how to use the windows calculator. I just thought it would be cool to have an equation that could potentialy calculate pi exactly, even though it would take an infinite amount of time.


The sum from n = 0 to INF of 1/n^2 is Pi^/6. Calculate the nth partial sum, multiply by 6, and take the square root. There you have an approximation to Pi. If you find a book on Fourier analysis you can find a bunch of other infinite series that converge to Pi.

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