# Tutor.com Quadratic Functions Session

##### Aug. 30, 2012

Session Transcript - Math - Algebra II, 8/27/2012 12:33AM - Tutor.comSession Date: 8/27/2012 12:33AM
Length: 15.6 minute(s)
Subject: Math - Algebra II

System Message
[00:00:00] *** Please note: All sessions are recorded for quality control. ***

Alexandria (Customer)
[00:00:00] what is the domain of the function? i can't get pass the bottom part

Glenn S (Tutor)
[00:00:35] Do you need the definition of the domain?

Alexandria (Customer)
[00:01:01] oh no, its the solving part..

Glenn S (Tutor)
[00:01:18] In general, it is the range of numbers for which it is defined, so basically, what numbers work in that function. Does that much make sense so far?

Alexandria (Customer)
[00:01:30] thats a 9 by the way
[00:01:31] yes

Glenn S (Tutor)
[00:02:26] OK, great. So, basically assume that all numbers work, then pick out those that clearly don't make sense, such as dividing by zero, since that would make the function infinite.
[00:02:46] So, do you think x=0 is ok for this function, or not?

Alexandria (Customer)
[00:03:34] yes?

Glenn S (Tutor)
[00:04:04] But the denominator is x*(x^2-36), so if x=0 what does the denominator equal?

Alexandria (Customer)
[00:04:41] oohh o
[00:04:43] 0
[00:05:00] so that wouldnt work sense you cant divide by zero right

Glenn S (Tutor)
[00:05:20] Right, now look at the x^2-36 part, so what x is bad for that?

Alexandria (Customer)
[00:05:49] X square?

Glenn S (Tutor)
[00:06:30] yes, notice the x squared is minus 36, so what if x squared = 36? Is that okay, or is that bad?

Alexandria (Customer)
[00:07:32] okay? cause then you can square root the x^2 and 36
[00:07:37] right?

Glenn S (Tutor)
[00:07:58] Yes, so the square root of 36 is what?

Alexandria (Customer)
[00:08:10] 6

Glenn S (Tutor)
[00:08:27] don't forget the negative, too, since squaring makes it positive.
[00:09:07] Now, plug in x=+-6 to the (x^2-36), what number do you get?

Alexandria (Customer)
[00:10:08] 0
[00:10:22] so -72?

Glenn S (Tutor)
[00:11:02] Yes, and anything divided by zero is BAD. No, 36-36=0, and that's not good, because it's in the denominator.
[00:11:38] The basic rule of all domains is that nothing bad can happen, so you can't divide by zero, you can't have an undefined result for the function.

Alexandria (Customer)
[00:11:49] okay

Glenn S (Tutor)
[00:12:09] So, now I think you have it, but please tell me then what numbers are NOT good for your function.

Alexandria (Customer)
[00:12:19] so is it x not equal to 0
[00:12:25] 0

Glenn S (Tutor)
[00:12:30] but what about the sixes?

Alexandria (Customer)
[00:12:44] its both right?

Glenn S (Tutor)
[00:13:51] any numbers are okay EXCEPT for the three bad ones.
[00:14:06] Got it?

Alexandria (Customer)
[00:14:10] yes

Glenn S (Tutor)
[00:14:19] Great. Nice work!
[00:14:55] Do you have any questions about anything we went over today?

Alexandria (Customer)
[00:15:16] no, thank you for your time

Glenn S (Tutor)
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