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Differential Equation (Solution known, but I don't understand)

by negatifzeo
Tags: differential, equation, solution
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negatifzeo
#1
Jan14-10, 02:25 PM
P: 66
1. The problem statement, all variables and given/known data
In this problem, a function y= g(x) is described. Write a differential equation of the form "dy/dx=f(x,y) having the function g as it's solution (or one of it's solutions).

The line tangent to the graph of g at the point (x,y) intersects the x-axis at the point (x/2,0).



2. Relevant equations



3. The attempt at a solution
The solution is y'=2y/x. I'm having trouble seeing both why and how.
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Dick
#2
Jan14-10, 02:34 PM
Sci Advisor
HW Helper
Thanks
P: 25,228
The tangent passes through a point on the curve, call it (x,y) and has a slope y'. That tangent also passes through (x/2,0). Express y' by finding the slope of the line through the two points (x,y) and (x/2,0).
negatifzeo
#3
Jan14-10, 02:36 PM
P: 66
Thank you so much!

Altabeh
#4
Jan14-10, 02:37 PM
P: 665
Differential Equation (Solution known, but I don't understand)

Quote Quote by negatifzeo View Post
1. The problem statement, all variables and given/known data
In this problem, a function y= g(x) is described. Write a differential equation of the form "dy/dx=f(x,y) having the function g as it's solution (or one of it's solutions).

The line tangent to the graph of g at the point (x,y) intersects the x-axis at the point (x/2,0).



2. Relevant equations



3. The attempt at a solution
The solution is y'=2y/x. I'm having trouble seeing both why and how.
Write the equation of line with m = g'(x), x0=x/2 and y0=0. Then try to recover that ODE.

AB


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