Perspective and geometrical drawing adapted to the use of candidates for second and third-class teachers' certificates . e to an ob-long. Triangles are equilateral, withthree equal sides; Isosceles, with two equal sides; Scalene, with unequal sides. Right angled, or containing aright angle; Obtuse angled, or containingan obtuse angle; Acute angled, or containingthree acute angles. To draw a triangle we firstdraw a plan^ showing the tri-angle and its bounding oblong. Thus, 1 would be a plan foran equilateral triangle ABC, inwhich D A = AE = BF = FC. 2 would be a plan for a right-angled triangle
Perspective and geometrical drawing adapted to the use of candidates for second and third-class teachers' certificates . e to an ob-long. Triangles are equilateral, withthree equal sides; Isosceles, with two equal sides; Scalene, with unequal sides. Right angled, or containing aright angle; Obtuse angled, or containingan obtuse angle; Acute angled, or containingthree acute angles. To draw a triangle we firstdraw a plan^ showing the tri-angle and its bounding oblong. Thus, 1 would be a plan foran equilateral triangle ABC, inwhich D A = AE = BF = FC. 2 would be a plan for a right-angled triangle, in which theangle hoc is theright angle, withhe as hypothenuse; the segments5/, fc of the hypothenuse woulddetermine the position of a. 40 DBA WING, In 3, the triangle DAC being given, CE would be drawnperpendicular to DA, and CB parallel to DA; also DB andAF would be drawn parallel to CE: then position o£ theangles at A and C would be easily dertermined. Example 1.—Draw an equilateral triangle, 2t to b, side,lying on ground, one side touching near left angle, 4 toright. Height 6, distance 4\ scale ^ = fig. 22, Draw , and as before. Take A i to right ofS, and B 3 to right of A; join A and B ; on ABdescribe equilateral triangle ABE (below AB). Draw AD,BF at right angles to AB, and through E, draw DF parallelto AB, and meeting AD in D and BF in F; draw EG paral-lel to AD. Join G , and with centre A and distanceAD, describe arc DL, cutting in L. Join UM, cutting THE TRIANGLE. 41 A C. V. in N; through N draw NK parallel to AB, cuttingG in C and B in K. Join CA and CB: thenABC is the triangle required. For AB = AE and AD = AL- AN = CG = height of triangle; also NC = CK = AG = GB =DE = EF. Then AC = AE = EB = BC, for they are diagonalsof equal oblongs. (Fig. 22.) In this figure the vertex C is directed away from the eye. If we joined NG and KG we would have a similar triangle,but with vertex G directed towards the observer. ExaT
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Keywords: ., bookcentury1800, booksubjectgeometricald, booksubjectperspective
