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## Homework Statement

Question 2.2

http://www.studyjapan.go.jp/en/toj/pdf/08-007.pdf

The picture is in the next page of the problem.

- k is the Coulomb constant.
- q+ is the charge at point A.
- q- is the charge at point B.
- AC = BC = CD = a

## Homework Equations

E = kq/d²

a² = b² + c²

## The Attempt at a Solution

I put the vectors on the force line at AD and DB, adding the vectors we get the eletric field at point D, the problem is that when I use a² = b² + c² (observe that is a right triangle) I get the result Kq/a, answer D, but the correct answer is B. Where is wrong?

I have just learned Electrostatics, maybe it is a simple problem, but I can not solve.

Thank you.