Geodesics and Motion in an EM Field

[Woolyabyss]

Homework Statement

I've attached the problem statement as an image.

Relevant Equations

Euler Lagrange equations

I've also attached my attempt as a pdf file. My main issue seems to be I only get one A partial term. Any help would be appreciated.

 

[Woolyabyss]

I've just realized my mistake. the partial of q A_b with respect to lambda isn't zero, you get an extra term from the chain rule and it works out nicely.