Posted by **trig** on Thursday, May 7, 2009 at 5:46pm.

study of sunspots. spots in a year min. is 10, max is 110. between max's of 1750 & 1948, 18 cycles occurred. Find a sinusoidal equation to model this.

My equation looks something like this so far:

y=50sin(2pi/11(x-d))+60

so How do I get the phase shift? d? I am confused about what would be x and y to plug into the formula and find d? Because the max occurs at 1750, but what would be the x and y values to sub in and why?

- Anonymous -
**Damon**, Thursday, May 7, 2009 at 5:58pm
y=50sin( 2pi(x-d)/11 )+60

when x = 1750, you have a max and sin (2 pi(1750-d)/11) = 1

or 2 pi (1750-d)/11 = pi/2 (90 degrees for max of sin function)

1750-d =11/4 (in other words a quarter of a cycle after start)

d = 1750 - 11/4

- Anonymous -
**trig**, Thursday, May 7, 2009 at 6:02pm
How did you get 1750-d=11/4?

- Anonymous -
**trig**, Thursday, May 7, 2009 at 6:10pm
I mean, so would d = 1747.25

ie

y=50sin(2pi/11(x-1747.25))+60

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