# sinusoidal function need help!

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• March 20th 2013, 04:40 AM
shanhuawu60474
sinusoidal function need help!
http://cdn.mathhelpforum.com/images/icons/icon4.png sinusoidal function need help!
need this asap for a test and i don't know how to solve it when it doesn't have an x in the equation

problem is : find the a, b, c ,d of y=25sin(1.3pi+0.4pi*t)+28

i know a is 25
d is 28
how to solve b and c?
• March 20th 2013, 04:43 AM
Shakarri
Re: sinusoidal function need help!
We don't know what a,b,c,d mean so we cant help you.
• March 20th 2013, 04:47 AM
shanhuawu60474
Re: sinusoidal function need help!
a is amplitude
b is period
c is phase shift
d is mean
• March 20th 2013, 04:47 AM
shanhuawu60474
Re: sinusoidal function need help!
a is amplitude
b is period
c is phase shift
d is mean
• March 20th 2013, 04:55 AM
shanhuawu60474
Re: sinusoidal function need help!
a is amplitude
b is period
c is phase shift
d is mean
• March 20th 2013, 05:21 AM
Shakarri
Re: sinusoidal function need help!
Try not to spam click when you post... you made 2 thread and now you posted the same thing 3 times.

When your function is in the form
$y= Msin(\theta t+ \phi)+j$ where k and j are constants
The maximum value of the sine of an angle is 1 so the maximum value of $sin(\theta t+ \phi)$ is just 1
The amplitude is the maximum value of the function which is $y= M\cdot 1+j$
So the amplitude is M+j not just the number in front of the sin.

The phase shift is the amount the angle is constantly shifted by, the phase shift is [tex]\phi[\tex]

The function repeats itself after the angle has gone through $2\pi$ radians. The period is how long it takes to go through $2\pi$ radians. This is the value of t so that $\theta t= 2\pi$

Since the sine of a changing angle is sometimes positive and sometimes negative the positives and negatives cancel out and the mean of $Msin(\alpha t)$ is 0. Where $\alpha$ is a constant.
As the mean of $Msin(\theta t+ \phi)$ is 0, the mean of $Msin(\theta t+ \phi)+j$ is j.
• March 22nd 2013, 11:56 PM
Debsta
Re: sinusoidal function need help!
In the form y=a sin b(x-c) +d ... b is NOT the period. b/(2pi) is the period.

Also t is the variable NOT x.