2.1.3 Doubling the point P To add a point P to itself, a tangent line to the curve is drawn at the point P. If yP is not 0, then the tangent line intersects the elliptic curve at exactly one other point, -R. -R is reflected in the x-axis to R. This operation is called doubling the point P; the law for doubling a point in an elliptic curve group is defined by: P + P = 2P = R.
2P = R
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