# Thread: How find the b in a sin equation?

1. ## How find the b in a sin equation?

Hi,
Can anyone tell me how to find the b in the sin model equation:
Asinb(x+c)+d

I'm trying to find the period of the function: which is 2*pi/b. Can anyone tell me how to find b.

2. $\displaystyle y = A\sin[B(x + C)] + D$

are you looking at a graph? you need the period to find the value of B.

3. Originally Posted by skeeter
$\displaystyle y = A\sin[B(x + C)] + D$

are you looking at a graph? you need the period to find the value of B.
Yes, I am looking at a graph. But how can I find the period without finding the value of B first?

4. then you should be able to determine the period from the graph.

once again, you need the period to find the value of B.

5. Originally Posted by skeeter
then you should be able to determine the period from the graph.

once again, you need the period to find the value of B.
But how do I find the period? I'm only looking at a small section of the graph.
I'm sorry if this is getting repetitive

7. Ok, hold on while I'll try to get it on here...

8. Well, if you have a graphing calculator, the function is
y= 10.1553107*sin(.3297896754x-2.618974022)+14.05881237

I'm sorry but I don't think there is a way to upload the graph; it's in a special program...but I'll keep trying!

9. Here it is!

10. Originally Posted by overduex
Well, if you have a graphing calculator, the function is
y= 10.1553107*sin(.3297896754x-2.618974022)+14.05881237

I'm sorry but I don't think there is a way to upload the graph; it's in a special program...but I'll keep trying!
your graph is made up from data points ... you have B

11. Originally Posted by skeeter
your graph is made up from data points ... you have B
Sorry, I may have made really things unclear. Our assignment is to find the sin equation by 2 methods: using the calculator and by hand.
I understand how to find the function using the calculator, but finding the equation of the function by hand is what I need help with.

I have found A or the amplitude, D, and C.
But I do not understand how to find B by hand. Our professor told us to use the period to find it, but I do not understand how to do that.
Does my question make sense now? How do I find B?

I really appreciate your help so far. Thanks

12. the horizontal distance from the very bottom of the curve to the very top of the curve is half the period.

just eyeballin' , but looks about 9.6 units of horizontal distance ... so the period is roughly double that ... 19.2 units.

you can probably be more accurate with a ruler.