Solving initial value problem of homogenous equation y' = (7 xy)/(7 x^(2)+2 y^(2)) using substitution.

bucstar11n0h

bucstar11n0h

Answered question

2022-11-12

Solving initial value problem of homogenous equation y = 7 x y 7 x 2 + 2 y 2 using substitution.
I am given the initial value problem
y = 7 x y 7 x 2 + 2 y 2 y ( 1 ) = 1
where I must answer in the form of F ( x , y ) = 7 4
Here, I am also asked to use the substitution y = x u to transform this differential equation into a separable differential equation in u. I am not sure how to go about doing this since I am not too familiar with differential equations. Any help would be greatly appreciated!

Answer & Explanation

merlatas497

merlatas497

Beginner2022-11-13Added 14 answers

Write y = u + u x and substitute in you equation, then
u + u x = 7 x ( u x ) 7 x 2 + 2 x 2 u 2 = 7 u 7 + 2 u 2
and
7 + 2 u 2 2 u 3 d u = d x x
7 2 u 3 d u + 1 u d u = d x x
7 4 u 2 + ln u = ln x + C
7 x 2 4 y 2 + ln y ln x = ln x + C
ln y = C + 7 x 2 4 y 2
set y ( 1 ) = 1 so C = 7 4 and ln y + 7 x 2 4 y 2 = 7 4

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