Point charges 1 nC and -1nC are located on a plane at lattice nodes with a cell in the shape of a square with side a=0.1 m. The lattice nodes in which the indicated charges are located are specified by radius vectors r1=(a,a), r2= (-a,a). There are no charges in the remaining nodes. Determine the strength and potential of the electric field at a point with radius vector r=(0,0).

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