72 The DoStrineL E M M A II.

The Latus-Rectum L , is to* anydouble Ordinate AM, (Fig* 11.) asRadius to the Tangent of the AngleMAt, which that double Ordinatemakes with the Tangent At to thePoint A.

DEMO N ST RAT 10 Ni

Let i>=:AM, r~ the Radius, Athe Height CV, and T the Tangent ,;

th en I b : 2 h \ :r:T‘. but b\ j\h\ :L:^,

( 7 %eo. 7.)consequently, L'.b::r:T.

L L. zx

THEOREM XIII.

In any Triangle inscrib’d in a Para-bola having a double Ordinate A M(Fig. 21.) for its Base, and its Vertex xany wherein the Curve above that Or-dinate,