# PI

Discussion in 'Math' started by lomax1, Feb 18, 2014.

1. ### lomax1 Thread Starter New Member

Feb 6, 2014
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I HAVE HAD THIS THROWN, KICKED AND EVEN SPAT AT ME BUT DOES NOT SEEM TO GO IN....

∏ (pi) if I have an equation 2∏t does this mean 2 of that number or 2 halves? so confused....

2. ### MrChips Moderator

Oct 2, 2009
12,633
3,453
It usually means two times pi times t

2 x ∏ x t

where ∏ = 3.141592653589793

Feb 6, 2014
27
0
(2∏t)
T

4. ### MrChips Moderator

Oct 2, 2009
12,633
3,453
Nice.

Usually T refers to the period of a repetitive signal
and t is a time variable.

Hence

t/T x 2∏

refers to the phase angle at time t where the phase angle is calculated in radians.

(There are 2∏ radians in 360 degrees or one period.)

5. ### lomax1 Thread Starter New Member

Feb 6, 2014
27
0
Great stuff, so 2∏50 = 100 ?
50 50

6. ### shteii01 AAC Fanatic!

Feb 19, 2010
3,500
511
2*pi*50/50=2*pi=2*3.14=6.28

100/50=2

7. ### MrChips Moderator

Oct 2, 2009
12,633
3,453
What?.......

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8. ### lomax1 Thread Starter New Member

Feb 6, 2014
27
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sorry, 2∏50/50 = 100/50

9. ### shteii01 AAC Fanatic!

Feb 19, 2010
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511
6.28 is not equal 2

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10. ### MrChips Moderator

Oct 2, 2009
12,633
3,453
No.

∏ has a value 3.141592654589793

You have to multiply 100/50 by 3.141592654589793

50/50 x 2 x pi = 2 ∏ radians = 360 degrees

11. ### t_n_k AAC Fanatic!

Mar 6, 2009
5,448
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Is this a novel method of teaching?

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12. ### lomax1 Thread Starter New Member

Feb 6, 2014
27
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So then, t= 0.002 Seconds, T(Tau)= 1.6 Seconds, T = 50 milliseconds and the equation is : y(t)=e-t/t(tau)sin(2∏t/T) It would be written as: e-0.002/1.6sin(2x50/∏)?

13. ### MrChips Moderator

Oct 2, 2009
12,633
3,453
No.

sin(2 pi t/T) = sin( 2 x 3.14159 x 0.002 / 0.050)

14. ### lomax1 Thread Starter New Member

Feb 6, 2014
27
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o...k, and the first bit before the sin is ok?

15. ### shteii01 AAC Fanatic!

Feb 19, 2010
3,500
511
Yes, it looks alright, the t is in seconds, the tau is in seconds. So you have: e to the power of -t/Tau
$e^{\frac{-t}{Tau}}=2.71^{\frac{-0.002}{1.6}}=0.998$
I think you can round it up to 1 or just keep 0.998 or 0.99

16. ### WBahn Moderator

Mar 31, 2012
18,087
4,917
Notice that you have

y(t)=e-t/t(tau)sin(2∏t/T)

This is very ill-formed. Strictly speaking, what you have written is

$
y(t) \; = \; e\,-\, $$\frac{t}{t}$$ \tau \, \sin $$\frac{2 \pi t}{T}$$
$

What I'm pretty sure you meant to write is

$
y(t) \; = \; e^{- \frac{t}{\tau}} \, \sin $$\frac{2 \pi t}{T}$$
$

which, in text, would be written as

y(t) = e^(- t/tau ) * sin(2∏t/T)