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#1 2014-11-20 06:03:39
- Whizzies
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- Registered: 2014-07-18
- Posts: 53
trigonometry the period!
Hello,
can someone explain to me the difference between multiplying relative to the y-axes and the period?
so sin (x) period is 2pi
multiply relative to the y-as with 3 than formula would be sin(x/3) and the period (2pi)/3 right?
I always mix them up and I don't know how to deal with it properly... could someone help?
thx
Last edited by Whizzies (2014-11-20 06:55:06)
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#2 2014-11-20 06:48:29
Re: trigonometry the period!
What does y-as mean here?
'And fun? If maths is fun, then getting a tooth extraction is fun. A viral infection is fun. Rabies shots are fun.'
'God exists because Mathematics is consistent, and the devil exists because we cannot prove it'
I'm not crazy, my mother had me tested.
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#3 2014-11-20 06:55:15
- Whizzies
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- Registered: 2014-07-18
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Re: trigonometry the period!
What does y-as mean here?
y axes sorry
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#4 2014-11-20 06:56:59
Re: trigonometry the period!
I do not understand.
Can you give an example?
'And fun? If maths is fun, then getting a tooth extraction is fun. A viral infection is fun. Rabies shots are fun.'
'God exists because Mathematics is consistent, and the devil exists because we cannot prove it'
I'm not crazy, my mother had me tested.
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#5 2014-11-20 07:00:55
Re: trigonometry the period!
Here is a good way to work out the period of a sinusoidal function of the form sin(w x) with independent variable x.
Call w angular velocity.
w=2pi/T
Hence, T = 2pi/w
'And fun? If maths is fun, then getting a tooth extraction is fun. A viral infection is fun. Rabies shots are fun.'
'God exists because Mathematics is consistent, and the devil exists because we cannot prove it'
I'm not crazy, my mother had me tested.
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#6 2014-11-20 22:28:25
- Bob
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- Registered: 2010-06-20
- Posts: 10,621
Re: trigonometry the period!
hi Whizzies
You'll probably find the MIF function grapher helpful:
http://www.mathsisfun.com/data/function … nc1=sin(x)
Enter sin(x/3) as the second graph and you'll see that the period gets bigger by a factor of 3, not smaller.
Think about it and maybe you can see why this is.
If x = pi/2, we know sin(x) = 1.
On the graph of sin(x/3), and to get sin(something) = 1, you need x/3 = pi/2, so x = 3pi/2. That is to say, you need an x value three times the size, to get a given y value on this graph.
eg. On y = sin(x) then x = pi/6 gives y = sin(pi/6) = 1/2
On y = sin(x/3) we need x = 3pi/6 to get y = sin(3pi/6 over 3) = sin(pi/6) = 1/2
I'm also looking at you symmetry post. I've never seen point symmetry written like this, so I'm having to work it out from scratch. Hopefully I'll get there soon. :)
Bob
Children are not defined by school ...........The Fonz
You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you! …………….Bob 
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#7 2014-11-21 21:55:29
- Whizzies
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- Registered: 2014-07-18
- Posts: 53
Re: trigonometry the period!
Thanks Guys (: I am understanding what it is that I am doing.
Like for example when I mulptiply the sin(x) with 2 I change the distance in respect to the y-axes, hence the period changes. The explanation was very clear Ty
I do have one question though!
In my book it is explained that:
g(2x)=f(x) <=> g(x)=f(x/2)
I understand what happens when you multiply by two, ut I don't understand why it could also be 1/2.
Last edited by Whizzies (2014-11-21 21:58:27)
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#8 2014-11-22 03:48:24
- Bob
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Re: trigonometry the period!
hi Whizzies,
g(2x)=f(x) <=> g(x)=f(x/2)
The first statement is true for all x. So you can replace x by x/2 and it will still be true.
Similarly, if the second statement is true for all x, then replace x by 2x and it will still be true.
Here's a simple example.
f(x) = 6x + 7 = 3 times (2x) +7
So we can define g by:
g(2x) = 3 times (2x) + 7
which means g(2x) = f(x)
The definition of g may also be written:
g(x) = 3x + 7 = 6 times (x/2) + 7 = f(x/2)
So g(x) = f(x/2)
Bob
Children are not defined by school ...........The Fonz
You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you! …………….Bob
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#9 2014-11-25 04:28:40
- Whizzies
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- Registered: 2014-07-18
- Posts: 53
Re: trigonometry the period!
I can follow that... but it is too much magic for me atm
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