Electric Potential at A and B: Find the Answer

[moeug1999]

Homework Statement

The figure below shows two point charges q1 = +5.4 10-8 C and q2 = -5.5 10-8 C.
(a) Find the potential at A
(b) Find the potential at B.

Relevant Equations

Coulombs Law

I found the potential at A, however I tried doing it with B but it says I have the wrong answer.

 

[gneill]

You'll have to show us the work on your attempt if we're to be able to help you.

 

[moeug1999]

here's my attempt for the first (which was correct) and for the second (which was wrong)

 

[gneill]

Can you provide some details about where the numbers come from in your calculations?

What formula are you using for electric potential? The basic Coulomb's Law gives the force between charges, not the potential due to a charge.