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The general solution of the differential equation dydx=eax+by\frac{dy}{dx} = e^{ax+by} is: (Here C is an arbitrary constant)

Solution

✅ Correct Option: 3

Given:

dydx=eax+by\frac{dy}{dx} = e^{ax+by}


Using the exponential property eA+B=eA⋅eBe^{A+B} = e^A \cdot e^B:

dydx=eax⋅eby\frac{dy}{dx} = e^{ax} \cdot e^{by}


Separating variables:

dyeby=eax dx\frac{dy}{e^{by}} = e^{ax} \, dx

e−by dy=eax dxe^{-by} \, dy = e^{ax} \, dx


Integrating both sides:

∫e−by dy=∫eax dx\int e^{-by} \, dy = \int e^{ax} \, dx

For the left side, using ∫eku du=ekuk\int e^{ku} \, du = \frac{e^{ku}}{k} with k=−bk = -b:

∫e−by dy=e−by−b\int e^{-by} \, dy = \frac{e^{-by}}{-b}

=−e−byb= -\frac{e^{-by}}{b}

For the right side, with k=ak = a:

∫eax dx=eaxa\int e^{ax} \, dx = \frac{e^{ax}}{a}


Combining results:

−e−byb=eaxa+C′-\frac{e^{-by}}{b} = \frac{e^{ax}}{a} + C'

Multiplying through by −ab-ab:

ae−by=−beax−abC′ae^{-by} = -be^{ax} - abC'

ae−by+beax=−abC′ae^{-by} + be^{ax} = -abC'

Since −abC′-abC' is an arbitrary constant, replacing it with CC:

ae−by+beax=Cae^{-by} + be^{ax} = C

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