Function Composition Math Example 4

Follow the full solution, then compare it with the other examples linked below.

Example 4

hard
Given f(x)=xf(x) = \sqrt{x} and g(x)=x2+5g(x) = x^2 + 5, find the domain of (fโˆ˜g)(x)(f \circ g)(x).

Solution

  1. 1
    (fโˆ˜g)(x)=f(g(x))=x2+5(f \circ g)(x) = f(g(x)) = \sqrt{x^2 + 5}.
  2. 2
    The square root requires x2+5โ‰ฅ0x^2 + 5 \geq 0. Since x2โ‰ฅ0x^2 \geq 0, we always have x2+5โ‰ฅ5>0x^2 + 5 \geq 5 > 0.
  3. 3
    The domain is all real numbers: (โˆ’โˆž,โˆž)(-\infty, \infty).

Answer

(โˆ’โˆž,โˆž)(-\infty, \infty)
When finding the domain of a composition, you must ensure both that the inner function is defined and that its output lies in the domain of the outer function.

About Function Composition

Function composition applies one function to the output of another: (fโˆ˜g)(x)=f(g(x))(f \circ g)(x) = f(g(x)), meaning evaluate gg first, then apply ff to the result.

Learn more about Function Composition โ†’

More Function Composition Examples