Higbee, F. G · New York, John Wiley & Sons · leaf 89
the planes is measured in aplane perpendicular to both planes or to their Hne of intersection.If, then, a plane be passed through any point of a Hne common 78 ESSENTIALS OF DESCRIPTIVE GEOMETRY to both planes and the intersection of this plane with both of theothers be found the angle thus formed… … Fig. 61. Assume the point 0 on the line common to the planes of the twosides, and through this point, by Article 48, pass a plane perpen-dicular to the line. This plane is rRr. Now by Article 54 findthe intersection of R and S, and R and T. This is OP in the firstcase and OQ in the second, and POQ…
Geometry, Descriptive
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