Mathematics 9709 · AS & A Level · Functions

Functions — practice question

(i)[3]

Write $2x^2 - 12x + 11$ in the form $a(x + b)^2 + c$, with $a$, $b$ and $c$ as constants.

(ii)[1]

The function $f$ is given by $f(x) = 2x^2 - 12x + 11$ for $x \le k$. State the greatest value of the constant $k$ that makes $f$ a one-one function.

(iii)[4]

For this value of $k$, find an expression for $f^{-1}(x)$ and state the domain of $f^{-1}$.

(iv)[3]

The function $g$ is defined by $g(x) = x + 3$ for $x \le p$. With $k$ now equal to $1$, find the largest value of the constant $p$ that permits the composite function $fg$ to be formed, and determine an expression for $fg(x)$ whenever this composite function exists.

Worked solution & mark scheme

This 11-mark question has a full step-by-step worked solution and mark scheme. One marking point: The correct factors $2$, $(x-3)^2$, $-7$ are shown.

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