Problem 16A, page 894
A diagram, showing the forces
on one wire, is to the right.
Each wire is in equilibrium.
Thus, the forces must add up to the null vector. Since the sum of the forces
must be the null vector, the vector diagram must close, as shown below:
Let x = the length of a wire
and 
, the mass per unit
length. Then...
Substituting the equation for
the force between two current-carrying conductors,
From the diagram we get an equation
for a:
Substituting this, we get
