trig functions translations and combinations of transfomations word problems

[Aka]

Hi, I really need help with this question

 

1) the water depth in a harber is 21m at hight tide, and 11m at low tide. One cycle is completed approximatly every 12h.

 

a) find an equation for the water depth as a function of the time, t hours, after low tide

b) Draw a graph 48h after low tide, witch occured at 14:00

 

y=asink(x-c)+d

 

Amplitude

a=21-11/2

a=5

 

K

 

p=2pi/k

12=2pi/k

k=2pi/12

k=pi/6

 

what about the c and the d??

 

and does anyone know of anygood software to graph trig functions?

 

Thanks

[hybrid04]

D is the vertical shift and c is the horizontal shift. Since the amplitude is 5 and the lowest level is 11, you just add 5 to that for d. c is the horizontal shift. Remember minus equals right so it would be something like 14 if your scale on the x axis was hours.

[Aka]

ok, thanks