Thread: Differential equation for straight lines through origin

Sketch a few members of the straight lines through the origin. By eliminating parameters, derive a differential equation which describes this family.

Attempt

(since there are infinite gradients)



but the correct answer was: . I am not sure why.

Well, your answer "dy/dx= m" isn't correct because you have not eliminated the parameter m!

From the original equation, y= mx, m= y/x which gives dy/dx= y/x.

Thanks. If instead the question was: find the differential equation for the straight lines through the point (2,3), what would the procedure be?

I tried using:

y = mx + c
3 = 2m + c

but differentiating it obviously wouldnt work, since there are only constants

Originally Posted by SyNtHeSiS

Thanks. If instead the question was: find the differential equation for the straight lines through the point (2,3), what would the procedure be?

I tried using:

y = mx + c .... (1)
3 = 2m + c .... (2)

but differentiating it obviously wouldnt work, since there are only constants

I have numbered the equations. Solve for c in terms of m from (2). Substitute this expression for c into (1). Now answer the question.