Solve the separable differential equation

hardatwork
Messages
9
Reaction score
0

Homework Statement



dx/dy=-0.6y
y(0)=5

Homework Equations





The Attempt at a Solution


I tried solving it by
\intdy/y=\int-0.6dx
ln(y)=-0.6x+c
ln(y(0))=-0.6(0)+c
ln(5)=c
ln(y)=-0.6x+ln(5)
y=e^{-0.6x}+5
But its incorrect. I don't know what I am doing wrong. Can someone helping see what I am doing wrong? Thank You so much!
 
Physics news on Phys.org
You should solve for your function before substituting initial conditions. Remember that e^{ln|y|}=y
 
hardatwork said:

Homework Statement



dx/dy=-0.6y

Is this a typo? Do really mean dx/dy=-0.6y, or do you mean dy/dx=-0.6y?

\intdy/y=\int-0.6dx
ln(y)=-0.6x+c
ln(y(0))=-0.6(0)+c
ln(5)=c
ln(y)=-0.6x+ln(5)
y=e^{-0.6x}+5
But its incorrect. I don't know what I am doing wrong. Can someone helping see what I am doing wrong? Thank You so much!

If \ln y=-0.6x+\ln 5, then

y=e^{-0.6x+\ln 5}=e^{\ln 5}e^{-0.6x}=5e^{-0.6x}\neq e^{-0.6x}+5
 
Okay. That makes so much sense. Thank You so much
 
There are two things I don't understand about this problem. First, when finding the nth root of a number, there should in theory be n solutions. However, the formula produces n+1 roots. Here is how. The first root is simply ##\left(r\right)^{\left(\frac{1}{n}\right)}##. Then you multiply this first root by n additional expressions given by the formula, as you go through k=0,1,...n-1. So you end up with n+1 roots, which cannot be correct. Let me illustrate what I mean. For this...
Back
Top