# When y= a constant, how do you find the interval of definition?

1. Jan 27, 2013

### Jeff12341234

I used the linear equation method to solve a D.E. and got y=3/4 at the end. I'm asked to find the interval of definition but I don't know how to do that when Y is just a constant :/

2. Jan 27, 2013

### Apteronotus

If your solution is y=c then dy/dt must have been 0.
Unless it was specified that dy/dt=0 on some particular interval, then your solution should be valid for all t.

3. Jan 27, 2013

### Jeff12341234

So the interval of definition would be (-∞,∞)?

I just don't get how a function can have a domain when it's just a constant...

4. Jan 27, 2013

### Mute

If your function is y(t) = 3/4, it means that for any t you give the function as an input, the function returns the value 3/4. So, the domain is whatever range of values of t you are allowed to put into your function. It doesn't matter that your function happens to return a constant in this case.

5. Jan 27, 2013

### Jeff12341234

thanks

6. Jan 28, 2013

### Staff: Mentor

Every function has a domain.
I wouldn't use the word "range" when you're talking about the domain, because of confusing the issue with the function's range.