The essentials of descriptive geometry . less axiomatic, andboth the proof and truth of these facts will be obvious as the study of the subjectprogresses, and may beproved by experimentas in Article 19. 24. To assume aplane, assimie any twotraces which are parallelto the G. L., or whichintersect the G. L. at acommon point. 25. To assume a linein a plane, assume eitherview of the Hne, as theplan view ab in Fig. plan view when ex-tended cuts the G. L. atm and cuts the H traceof the plane at n. Sincen is on the H trace itselevation will be on theG. L. at n; and since m ^° ^^ is on the G. L
The essentials of descriptive geometry . less axiomatic, andboth the proof and truth of these facts will be obvious as the study of the subjectprogresses, and may beproved by experimentas in Article 19. 24. To assume aplane, assimie any twotraces which are parallelto the G. L., or whichintersect the G. L. at acommon point. 25. To assume a linein a plane, assume eitherview of the Hne, as theplan view ab in Fig. plan view when ex-tended cuts the G. L. atm and cuts the H traceof the plane at n. Sincen is on the H trace itselevation will be on theG. L. at n; and since m ^° ^^ is on the G. L., m — rsince the Hne AB is to be in the plane T — must He on the Vtrace, mn, therefore, is the elevation and mn the plan of MNlying in the plane T. ab and ab are, of course, on mn andmn and are the plan and elevation of a Hne AB l5dng in theplane T. 26. To assume a point in a plane.—One method is to assumea Hne in the plane — as in the foregoing article — and on thisHne assume the point. Another method more convenient to use. PLANES 31 is to assume one view of the point — as the plan view a in — and through this assumed plan view of the point draw theplan mn of a line MN parallel to the H trace. Since this lineMN is parallel to the H trace its elevation will be parallel to the
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