Differential Equations Question 108

Question: The differential equation corresponding to primitive $ y=e^{cx} $ is or The elimination of the arbitrary constant m from the equation $ y=e^{mx} $ gives the differential equation

[MP PET 1995, 2000; Pb. CET 2000]

Options:

A) $ \frac{dy}{dx}=( \frac{y}{x} )\log x $

B) $ \frac{dy}{dx}=( \frac{x}{y} )\log y $

C) $ \frac{dy}{dx}=( \frac{y}{x} )\log y $

D) $ \frac{dy}{dx}=( \frac{x}{y} )\log x $

Show Answer

Answer:

Correct Answer: C

Solution:

$ y=e^{mx} $

Therefore $ \log y=mx\Rightarrow m=\frac{\log y}{x} $

Now $ y=e^{mx} $

Therefore $ \frac{dy}{dx}=me^{mx}=\frac{\log y}{x}.y=( \frac{y}{x} )\log y $ .