Exam-Style Problems

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June 2018 p11 q9
792

Functions f and g are defined for \(x \in \mathbb{R}\) by

\(f : x \mapsto \frac{1}{2}x - 2\),

\(g : x \mapsto 4 + x - \frac{1}{2}x^2\).

(i) Find the points of intersection of the graphs of \(y = f(x)\) and \(y = g(x)\).

(ii) Find the set of values of \(x\) for which \(f(x) > g(x)\).

(iii) Find an expression for \(fg(x)\) and deduce the range of \(fg\).

The function \(h\) is defined by \(h : x \mapsto 4 + x - \frac{1}{2}x^2\) for \(x \geq k\).

(iv) Find the smallest value of \(k\) for which \(h\) has an inverse.

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Feb/Mar 2018 p12 q10
793

Functions \(f\) and \(g\) are defined by

\(f(x) = \frac{8}{x-2} + 2\) for \(x > 2\),

\(g(x) = \frac{8}{x-2} + 2\) for \(2 < x < 4\).

(i) (a) State the range of the function \(f\). [1]

(b) State the range of the function \(g\). [1]

(c) State the range of the function \(fg\). [1]

(ii) Explain why the function \(gf\) cannot be formed. [1]

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Nov 2016 p13 q8
794

(i) Express \(4x^2 + 12x + 10\) in the form \((ax + b)^2 + c\), where \(a, b\) and \(c\) are constants.

(ii) Functions \(f\) and \(g\) are both defined for \(x > 0\). It is given that \(f(x) = x^2 + 1\) and \(fg(x) = 4x^2 + 12x + 10\). Find \(g(x)\).

(iii) Find \((fg)^{-1}(x)\) and give the domain of \((fg)^{-1}\).

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June 2016 p13 q10
795

The function f is such that \(f(x) = 2x + 3\) for \(x \geq 0\). The function g is such that \(g(x) = ax^2 + b\) for \(x \leq q\), where \(a, b\) and \(q\) are constants. The function fg is such that \(fg(x) = 6x^2 - 21\) for \(x \leq q\).

(i) Find the values of \(a\) and \(b\).

(ii) Find the greatest possible value of \(q\).

It is now given that \(q = -3\).

(iii) Find the range of \(fg\).

(iv) Find an expression for \((fg)^{-1}(x)\) and state the domain of \((fg)^{-1}\).

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