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1.5.8 Composite and inverse functions (A-level only)

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Question 55

An environmental study models the concentration of a chemical byproduct, CCC, in mg/L, as a function of the distance xxx, in km, from the source of the spill. The concentration is given by the function:

C(x)=5x−2x−4,x>4 C(x) = \frac{5x - 2}{x - 4}, \quad x > 4 C(x)=x−45x−2​,x>4
a.

Use calculus to prove that CCC is a decreasing function for its entire domain.

[3]
b.

Find an expression for the inverse function C−1(x)C^{-1}(x)C−1(x).

[3]
c.

Show that the composite function C(C(x))=ax+bx+cC(C(x)) = \frac{ax + b}{x + c}C(C(x))=x+cax+b​ where a,b,a, b,a,b, and ccc are constants to be determined.

[4]
d.

Deduce the range of C(C(x))C(C(x))C(C(x)).

[2]

1.5.8 Composite and inverse functions (A-level only) Questions

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