i have the equation
(x+2y) * y' = y
do i use a linear substitution or homogeneous substitution?
(x+2y) * y' = y
do i use a linear substitution or homogeneous substitution?
-
(x + 2y) y ' = y
divide by x
(1 + 2y/x) y ' = y/x
let y/x = v
y = vx
y ' = v + xv '
(1 + 2v)(v + xv ' ) = v
=> v + xv ' = v /(1 + 2v)
=> xv ' = v /(1+2v) - v
=> xv ' = ( v - v - 2v^2)/(1 + 2v)
=> xv ' = - 2v^2 /(1 + 2v)
separating variables
[(1 + 2v)/v^2 ] dv = -2 dx/x
=> [ (1/v^2) + (2/v) ] dv = -2 dx/x
integrating
=> -(1/v ) + 2 ln v = -2 ln x + c
=> 2 ln v + 2 ln x = c + (1/v)
=> v^2 x^2 = Ce^(1/v)
substitute v = y/x
=> y^2 = C e^(x/y)
=> y = K√e^(x/y)
divide by x
(1 + 2y/x) y ' = y/x
let y/x = v
y = vx
y ' = v + xv '
(1 + 2v)(v + xv ' ) = v
=> v + xv ' = v /(1 + 2v)
=> xv ' = v /(1+2v) - v
=> xv ' = ( v - v - 2v^2)/(1 + 2v)
=> xv ' = - 2v^2 /(1 + 2v)
separating variables
[(1 + 2v)/v^2 ] dv = -2 dx/x
=> [ (1/v^2) + (2/v) ] dv = -2 dx/x
integrating
=> -(1/v ) + 2 ln v = -2 ln x + c
=> 2 ln v + 2 ln x = c + (1/v)
=> v^2 x^2 = Ce^(1/v)
substitute v = y/x
=> y^2 = C e^(x/y)
=> y = K√e^(x/y)
-
(x + 2y) * y' = y
Dividing both sides by x:
y' + (2y/x)y' = y/x
Using the substitution v = y/x
xv' + v = y'
xv' + v + 2v*(xv' + v) = v
xv'(2v + 1) + v + 2v² = v
xv'(2v + 1) = -2v²
(2v + 1)/(-2v²) dv = dx/x
Integrating both sides:
-ln|v| + 1/(2v) = ln|x|
-ln|y/x| + x/(2y) = ln|x|
ln(y) = x/(2y)
Dividing both sides by x:
y' + (2y/x)y' = y/x
Using the substitution v = y/x
xv' + v = y'
xv' + v + 2v*(xv' + v) = v
xv'(2v + 1) + v + 2v² = v
xv'(2v + 1) = -2v²
(2v + 1)/(-2v²) dv = dx/x
Integrating both sides:
-ln|v| + 1/(2v) = ln|x|
-ln|y/x| + x/(2y) = ln|x|
ln(y) = x/(2y)