Just for brain refreshing

Problem :

In the Figure, particle 1 of charge q1 = -9.00q and particle 2 of charge q2 = +2.00q are fixed to an x axis. As a multiple of distance L, at what coordinate on the axis is the net electric field of the particles zero and plot  the strength of the  electric field as a function of position.

Solution :

Take an arbitrary position x which for the heck of coordinate  that is grester than L. Then,

We can look at this as a function of a and just plot the quantity in bracket (let’s use Excel for example). Can you show the graph of this problem ? Explain your answer !