Range or domain from dy/dx

A question is this type if and only if it asks to find the range of x or y values for which the curve is defined or has certain properties, using the derivative.

2 questions · Challenging +1.2

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Edexcel P3 2022 January Q10
7 marks Challenging +1.2
10. \begin{figure}[h]
\includegraphics[alt={},max width=\textwidth]{f3272b4c-d8dc-4f32-add9-153de90f4d0a-30_661_743_210_603} \captionsetup{labelformat=empty} \caption{Figure 3}
\end{figure} Figure 3 shows a sketch of the curve \(C\) with equation $$x = y \mathrm { e } ^ { 2 y } \quad y \in \mathbb { R }$$
  1. Show that $$\frac { \mathrm { d } y } { \mathrm {~d} x } = \frac { y } { x ( 1 + 2 y ) }$$ Given that the straight line with equation \(x = k\), where \(k\) is a constant, cuts \(C\) at exactly two points,
  2. find the range of possible values for \(k\).
Edexcel P4 2023 January Q5
7 marks Challenging +1.2
5. \begin{figure}[h]
\includegraphics[alt={},max width=\textwidth]{c46ca445-cf59-4664-931e-add9f2f81851-14_940_881_251_593} \captionsetup{labelformat=empty} \caption{Figure 2}
\end{figure} Figure 2 shows a sketch of the curve with equation $$y ^ { 2 } = 2 x ^ { 2 } + 15 x + 10 y$$
  1. Find \(\frac { \mathrm { d } y } { \mathrm {~d} x }\) in terms of \(x\) and \(y\). The curve is not defined for values of \(x\) in the interval ( \(p , q\) ), as shown in Figure 2.
  2. Using your answer to part (a) or otherwise, find the value of \(p\) and the value of \(q\).
    (Solutions relying entirely on calculator technology are not acceptable.)