Edexcel AEA 2019 June — Question 3

Exam BoardEdexcel
ModuleAEA (Advanced Extension Award)
Year2019
SessionJune
TopicFirst order differential equations (integrating factor)

3.Given that \(\phi = \frac { 1 } { 2 } ( \sqrt { 5 } + 1 )\) ,
(a)show that
(i)\(\phi ^ { 2 } = \phi + 1\)
(ii)\(\frac { 1 } { \phi } = \phi - 1\)
(b)The equations of two curves are $$\begin{array} { r l r l } y & = \frac { 1 } { x } & x > 0
\text { and } & y & = \ln x - x + k & x > 0 \end{array}$$ where \(k\) is a positive constant.
The curves touch at the point \(P\) .
Find in terms of \(\phi\)
(i)the coordinates of \(P\) ,
(ii)the value of \(k\) .