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Question 29296: what is a domain ?
Answer by longjonsilver(2297)   (Show Source):
You can put this solution on YOUR website! the domain of the function f(x) is all the values of x that you are allowed to put into the function, beit from the questioner or from the physical nature of the function.
eg y=2x-3. Put in the values x=3 and x=14 into this. Here the domain is 3 and 14 because i have told you it.
eg What is the domain of y=3x+2? Well, this is a straight line, so any value of x that i pick will "work" ie give me an answer, so here, the answer is:
"the domain is any value of x"
being more strict, we are interested in the "REAL set of numbers" ie every number you can think of (not imaginary ones), so strictly we say:
"the domain is any value of x where x belongs to the Real set of numbers"
mathematically we don't want to write all this every time so we have a short hand:
"the domain is any value of x where x belongs to the Real set of numbers"
"the domain is xeR" where e means "belongs to" and R means "the Real set of numbers"
eg find the domain of y=1/x.
Now, you need to know what 1/x looks like...sketch it and learn its shape. The critical point to note is that when x=0, we get 1/0 which is infinity...it is a non-defined value for this function.
So, the domain here is "x belongs to the Real set, but not zero". Mathematically, this is:
"xeR, x = 0 " --> put a line through the "=" sign, to donote "not equal to"...i cannot do it on here.
Hope this helps.
jon.
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