bac-s-maths 2015 Q3

bac-s-maths · France · liban 3 marks Tangents, normals and gradients Prove a given line is tangent to a curve
We consider the curve $\mathscr{C}$ with equation $y = \mathrm{e}^{x}$.
For every strictly positive real $m$, we denote by $\mathscr{D}_{m}$ the line with equation $y = mx$.
  1. In this question, we choose $m = \mathrm{e}$.
    Prove that the line $\mathscr{D}_{\mathrm{e}}$, with equation $y = \mathrm{e}x$, is tangent to the curve $\mathscr{C}$ at its point with abscissa 1.
  2. Conjecture, according to the values taken by the strictly positive real $m$, the number of intersection points of the curve $\mathscr{C}$ and the line $\mathscr{D}_{m}$.
  3. Prove this conjecture.
We consider the curve $\mathscr{C}$ with equation $y = \mathrm{e}^{x}$.

For every strictly positive real $m$, we denote by $\mathscr{D}_{m}$ the line with equation $y = mx$.

\begin{enumerate}
  \item In this question, we choose $m = \mathrm{e}$.

Prove that the line $\mathscr{D}_{\mathrm{e}}$, with equation $y = \mathrm{e}x$, is tangent to the curve $\mathscr{C}$ at its point with abscissa 1.
  \item Conjecture, according to the values taken by the strictly positive real $m$, the number of intersection points of the curve $\mathscr{C}$ and the line $\mathscr{D}_{m}$.
  \item Prove this conjecture.
\end{enumerate}