Determining Domain problem??

Posted on Mar 25, 2008 under domain news and reports | 7 Comments

Could u plzzzz help me solve the following…any help would be highly appreciated

Let f(x) = sqrt(16 – x) and g(x) = x^4. What is the domain of each of the following?

(a) f

(b) f o g

(c) g o f

Thanx very much in advance

7 Responses to “Determining Domain problem??”

  1. notthejake Says:

    1) you can't take the square root of a negative number, so 16 – x >= 0, or x <= 16 (-inifinity,16] in interval notation

    2) because f(g) is sqrt(16 – g) you can replace x with g in the domain above:
    g<= 16
    but we know g = x^4, so x^4 <= 16
    take fourth root of both sides, and remember the inequality:
    -2 <= x <= 2 (or [-2,2])

    the domain of g is all real numbers, so that doesn't limit the domain any

    c) domain of g is all real numbers.
    since g(f) must be defined, that means f must be defined, and the domain of this composite is the same as the domain of f: x <= 16 (-infinity, 16]

  2. Scranderberry Says:

    The domain is the x values for which the function exists.

    f(x) = sqrt(16 – x)
    this works only when 16-x is positive so 16-x>0
    x<16 (x is an element of the reals)

    g(x) = x^4.

    fog = f(x^4)=sqrt(16 – x^4)
    which works when 16-x^4 >0
    x^4<16
    -2<x<2 (x is an element of the reals)

    gof=g(sqrt(16 – x))=sqrt(16 – x)^4
    =(16-x)^2
    this is do-able for all values of x

    or x is any real

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