| Exam Board | Edexcel |
| Module | AEA (Advanced Extension Award) |
| Year | 2019 |
| Session | June |
| Topic | First 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 \(k\) .