Bailey, Frederick H. (Frederick Harold), 1865- · Boston, London, Ginn & Co. · leaf 217
ated applicationsof this process give as many points as are wished. (2) By a mechanical device. Find the foci by § 93, if theyare not already given. Fix a pin at each focus and attach toeach pin one end of a thread of length 2a. Place the pointof a pencil in the loop of the thread and move it so as… … Fig. 89. THE ELLIPSE. 203 Let TT be a tangent, Pi(xi, yi) the point of tangency, andFPi and FPi the focal radii of Pi. To proveZFPiT^ZFPiT.Draw the normal, PiR. By (2), § 77, its equation is Call CR its intercept on the axis of x ; then, placing y ^= 0, we find ro a-—b- CK = :;— Xi = e-Xi. a Hence…
Geometry, Analytic
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