Question
Obtain the differential equation by eliminating arbitrary constants from the following equations : $y=A e^{3 x}+B e^{-3 x}$

Answer

$
y=A e^{3 x}+B e^{-3 x}
$
Differentiating twice w.r.t. $x$, we get
$
\begin{aligned}
& \frac{d y}{d x}=A e^{3 x} \times 3+B e^{-3 x} \times(-3) \\
& \begin{aligned}
\therefore \frac{d y}{d x}= & 3 A e^{3 x}-3 B e^{-3 x} \\
\text { and } \frac{d^2 y}{d x^2} & =3 A e^{3 x} \times 3-3 B e^{-3 x} \times(-3) \\
& =9 A e^{3 x}+9 B e^{-3 x} \\
& =9\left(A e^{3 x}+B e^{-3 x}\right)=9 y
\end{aligned} \\
& \begin{aligned}
\therefore \frac{d^2 y}{d x^2} & =9 y
\end{aligned}
\end{aligned}
$
This is the required D.E.

Need a full question paper?

Generate a complete, print-ready paper with questions like this in minutes — across 16+ boards, with answer keys.

Start Generating Free