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Solve the initial value problem: dydx+5y=7 y(0)=0

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Answer:

Given differential equation,


(dy)/(dx)+5y=7


(dy)/(dx)=7-5y


\implies (dy)/(7-5y)=dx

Taking integration both sides,


\int (dy)/(7-5y)=\int dx

Put 7 - 5y = u ⇒ -5 dy = du ⇒ dy = -du/5,


-(1)/(5) \int (du)/(u) = \log x + C


-(1)/(5) \log u = \log x + C


-(1)/(5)\log(7-5y) = \log x + C---(1)

Here, x = 0, y = 0


\implies -(1)/(5) \log 7= C

Hence, from equation (1),


-(1)/(5)\log(7-5y)=\log x -(1)/(5)log 7


\log(7-5y)=\log ((x)/(7^(1)/(5)))


7-5y=(x)/(7^(1)/(5))


7-(x)/(7^(1)/(5))=5y


\implies y=(1)/(5)(7-(x)/(7^(1)/(5)))

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