# Periodic Functions - Applications

• Dec 6th 2012, 03:40 PM
sakonpure6
Periodic Functions - Applications
I have the following equation $y= -4sin15x+25$ ( y represents the temperature and x represents time in hours, so x=0 means midnight and x=1 means 1:00 am) and I am given a question with the graph of the given equation, and to get the solution to the question you can you use the graph (which is also what my teacher told us to do) and so i do use the graph and get the correct answer of 13 hours. My question is how would i use the equation to solve for what i need?

The question:

The pool is comfortable for swimming at 23 degrees Celsius. The pool is open from 6:00 am to 11:00 pm. How many hours of comfortable swimming are available on a sunny day?

Any help is appreciated and thank you in advance!
• Dec 6th 2012, 04:17 PM
chiro
Re: Periodic Functions - Applications
Hey sakonpure6.

For this problem you will need to say what values of y can be taken.

You mention 23 degrees but are you allowed to have a range of values (like less than 23 degrees or greater than 23 degrees)?

Once you have this you solve your inequality.
• Dec 6th 2012, 06:26 PM
sakonpure6
Re: Periodic Functions - Applications
Quote:

Originally Posted by chiro
Hey sakonpure6.

For this problem you will need to say what values of y can be taken.

You mention 23 degrees but are you allowed to have a range of values (like less than 23 degrees or greater than 23 degrees)?

Once you have this you solve your inequality.

no y must be exactly 23 degrees
• Dec 6th 2012, 07:39 PM
chiro
Re: Periodic Functions - Applications
Well can you set y to 23 and solve for x?
• Dec 7th 2012, 06:43 AM
sakonpure6
Re: Periodic Functions - Applications
Oh sorry y must be 23 degrees untill the peak shich is what i believe to be 29
• Dec 7th 2012, 01:15 PM
chiro
Re: Periodic Functions - Applications
Can you setup an inequality where you solve for y = 29 and y = 23 to get the values inbetween?
• Dec 7th 2012, 05:13 PM
sakonpure6
Re: Periodic Functions - Applications
Quote:

Originally Posted by chiro
Can you setup an inequality where you solve for y = 29 and y = 23 to get the values inbetween?

I don't know what "inequality" is, do you mind if you show me the equations?
• Dec 7th 2012, 05:43 PM
HallsofIvy
Re: Periodic Functions - Applications
Well, the point of an "inequality is that it isn't an equation!

If what you have told us is correct, you want $23\le -14 sin(15x)+ 25\le 29$. And the simplest way to solve that is to solve the equations -14 sin(15x)+ 25= 23 and -14sin(15x)+ 25= 29. The correct range for x will be between those values.
• Dec 7th 2012, 06:10 PM
sakonpure6
Re: Periodic Functions - Applications
Quote:

Originally Posted by HallsofIvy
Well, the point of an "inequality is that it isn't an equation!

If what you have told us is correct, you want $23\le -14 sin(15x)+ 25\le 29$. And the simplest way to solve that is to solve the equations -14 sin(15x)+ 25= 23 and -14sin(15x)+ 25= 29. The correct range for x will be between those values.

Oh okay thank you! Ill do them and compare my answers!