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Math Help - Range and Domain

  1. #1
    Member srirahulan's Avatar
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    Post Range and Domain

    f(x)=\left\{\begin{array}{cc}2,&\mbox{if}x\leq -3\\2x+3, & \mbox{if}-3<x<0\\1, &\mbox{if}x\geq \end{array}\right.


    In This function How can i find the domain and Range of f(x)

    should i go through the graph method or any other method.please explain how can i do this?
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  2. #2
    MHF Contributor

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    Re: Range and Domain

    Do you know what "domain" and "range" mean?? The domain of a function, f(x), is the set of all possible values of x. Some times that is specified explicitely. For example, if I define "f(x)= x^2 for x> 0". That tells me directly that the domain is x> 0. If it is not given explicitely, if we are just given a formula, it is the set of all values of x for which we can use the formula. If f is given by " f(x)= \frac{x- 3}{x+ 2}", I see that I can calculate that for every value of x except x= -2 because if x= 2, I would be dividing by 0 which is undefined. Here, we are told that is x\le -3, f(x)= 2. Okay, that's a constant and certainly exists for all such x. I can see that is -3< x< 0, f(x)= 2x+ 3. That can be calculated for all such x. Finally, we are told that if x\ge 0 (that value is missing but I assume that is what is meant) f(x)= 1. Again a constant and "calculable" for all such x. Since the three intervals, x\le -3, -3< x< 0, and 0\le x include all numbers, the domain is "all real numbers".

    The "range" is the set of all function values- if we write y= f(x), then it is the set of all y values. Obviously "2" and "1" are values of the function. The middle part, y= 2x+ 3, is a linear function from y= f(-3)= -6+ 3= -3 to y= f(0)= 3. That is, all numbers between -3 and 3 are values of y and so in the domain. Since 2 and 1 are in that set, we don't need to mention them separately. The range is " -3\le y\le 3" or, in interval notation, [-3, 3].
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  3. #3
    Member srirahulan's Avatar
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    Re: Range and Domain

    Thank you for you explain and i understand.
    Thanks....
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