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Continued thread

Proposition 36: If a point is marked without a circle whence two lines are drawn to the circumference, one cutting and the other applied to the circumference, and that made from the whole of the secant drawn according to the extrinsic part of it is equal to that made from the applied line drawn according to itself, from necessity the applied line will be touching the circle.

& that's book III. which was honestly pretty good. comparatively.

IV contd: no-outlet.com/@ivlia/113964625

Continued thread

Proposition 35: If a point is marked without a circle whence two straight lines are drawn to the circle, with one line cutting and the other touching, then that contained within the whole secant as well the extrinsic part of it, is equal to the quadrate that is drawn from the tangent line.

Continued thread

Proposition 31: If a straight line contacts a circle and from the point of contact an other straight line is drawn within the circle, dividing the circle off center, whatever two angles it makes at the tangent are equal to the two angles that are over the arc in alternate portions of the circle.

Continued thread

Proposition 30: If a rectilinear angle in a semicircle rests upon the arc, it is right. And if it's in a portion less than a semicircle, it's greater than right. And if it's in a portion greater than a semicircle, it's less than right. Furthermore, the angle of any portion greater than a semicircle will be greater than right and by necessity, that of a lesser portion will be less than right.

Continued thread

Proposition 27: If equal lines resect arcs within equal circles, the arcs too shall be equal. And if the lines are not equal then the arcs too shall not be equal, and it is necessary for a greater arc to be abscinded by a greater line and a lesser arc by a lesser line.