From external point (x1,y1) to $y^2$=4ax: chord of contact is T=0 (yy1=2a(x+x1)), chord with midpoint is T=S1, pair of tangents is $T^2$=S*S1. These are the same T=0 substitution rules used for circles and all conics. The area of the triangle formed by the tangent pair and chord of contact from point P equals S1^$\frac{3/2}{(2a)}$ (where S1 is the power of the point). The pole of a line with respect to the parabola is found by comparing the polar equation with the given line. The polar of the focus is the directrix, a fundamental result connecting pole-polar theory with the definition.