Determining Domain problem??
Posted on Mar 25, 2008 under domain news and reports | 7 CommentsCould 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

March 25th, 2008 at 7:29 am
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]
March 25th, 2008 at 7:29 am
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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