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## Homework Statement

Two charges q = 9.0μ

*C*are fixed in space a distance d = 1.5

*cm*apart, as shown in the figure.

a) With V = 0 at infinity, what is the electric potential at point C?

b) You bring a third charge q = 9.0μC from infinity to C. How much work must you do?

c) What is the potential energy U of the three-charge configuration when the third charge is in place?

## Homework Equations

electrical potential=kq/r

μ=E-6

q=9E9

## The Attempt at a Solution

I thought that I should find the distance between q and C using the pythagorean theorem.

((9E9)(9.0E-6)/(2.1213 cm))+((9E9)(9.0E-6)/(2.1213 cm))=7.64E4 V

But this didn't work. The online homework said it was wrong.

Is that the right equation to use? How does the V=0 at infinity affect this problem?