# Thread: sinusoidal function need help!

1. ## sinusoidal function need help!

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?

3. ## Re: sinusoidal function need help!

a is amplitude
b is period
c is phase shift
d is mean

4. ## Re: sinusoidal function need help!

a is amplitude
b is period
c is phase shift
d is mean

5. ## Re: sinusoidal function need help!

a is amplitude
b is period
c is phase shift
d is mean

6. ## 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
$\displaystyle y= Msin(\theta t+ \phi)+j$ where k and j are constants
The maximum value of the sine of an angle is 1 so the maximum value of $\displaystyle sin(\theta t+ \phi)$ is just 1
The amplitude is the maximum value of the function which is $\displaystyle y= M\cdot 1+j$
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 $\displaystyle 2\pi$ radians. The period is how long it takes to go through $\displaystyle 2\pi$ radians. This is the value of t so that $\displaystyle \theta t= 2\pi$

Since the sine of a changing angle is sometimes positive and sometimes negative the positives and negatives cancel out and the mean of $\displaystyle Msin(\alpha t)$ is 0. Where $\displaystyle \alpha$ is a constant.
As the mean of $\displaystyle Msin(\theta t+ \phi)$ is 0, the mean of $\displaystyle Msin(\theta t+ \phi)+j$ is j.

7. ## 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.