MCQ
Choose the correct answer from the given four option.
$\text{y}= \text{a}\text{e}^{\text{mx}}+\text{b}\text{e}^{-\text {mx}}$ satisfies which of the following differential equation?
  • A
    $\frac{\text{dy}}{\text{dx}}+\text {my}=0$
  • B
    $\frac{\text{dy}}{\text{dx}}-\text {my}=0$
  • $\frac{\text{d}^2\text{y}}{\text{dx}^2}-\text{m} ^2\text{y}=0$
  • D
    $\frac{\text{d}^2\text{y}}{\text{dx}^2}+\text{m} ^2\text{y}=0$

Answer

Correct option: C.
$\frac{\text{d}^2\text{y}}{\text{dx}^2}-\text{m} ^2\text{y}=0$
Given that, $\text{y}=\text{a}\text{e}^{\text{mx}}+\text{b}\text{e}^{- \text{mx}}$

On differentiating both sides w.r.t.x, we get

$\frac{\text{dy}}{\text{dx}}=\text {ma}\text{e}^{\text{mx}}+\text{bm}\text{e}^{-\text {mx}}$

Again, differentiating both sides w.r.t.x, we get

$\frac{\text{d}^2\text{y}}{\text {d}\text{x}^2}=\text{m}^2\text{a}\text{e}^{\text{mx}}+ \text{b}\text{m}^2\text{e}^{-\text{mx}}$

$\Rightarrow\frac{\text{d}^2\text {y}}{\text{d}\text{x}^2}=\text{m}^2(\text{a}\text{e}^{\text {mx}}+\text{b}\text{e}^{-\text{mx}})$

$\Rightarrow\frac{\text{d}^2\text {y}}{\text{d}\text{x}^2}=\text{m}^2\text{y}$

$\Rightarrow\frac{\text{d}^2\text {y}}{\text{d}\text{x}^2}-\text{m}^2\text{y}=0$

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