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has compound curved surfaces convex and concave combined with a flat one its base yet it can all be made, if necessary, though at a great waste of material, out of a single flat plate, its sides being after- wards bent to the shape required. 86. As the whole, or a part of the surface of another plane solid, the " oblique pyramid " (which often contributes in giving form to plate and other metal structures), is rather more difficult of development than that of a " right pyramid " on account of its frequent great inclination from the vertical the solution of the next problem will show how its correct development may be found with the least number of construc- tion lines. Problem 92 (Fig. 196). Given the elevation of an oblique square pyramid, to find the development of its side surfaces, when its axis is inclined 45 from the vertical; also the development of the surface of a frustum of the same pyramid, of a given vertical height. Let ABC, No. 1 (Fig. 196), be the elevation of the pyramid. As all its sides with their edges are inclined to both the VP and HP, it is evident that the actual shape of the whole or any part of its surface, cannot be found by direct projection, or from the elevation alone, without a plan of the solid. Now although an oblique pyramid differs from a right one, in having its axis inclined to its base it must be remembered that any section of it parallel to its base is still as in the case of a right pyramid of the same/orm as its base. Bearing this in mind, there will be no difficulty in solving the given problem, more particularly the latter part of it. The elevation of the pyramid being given, find by projection a plan of it, as shown in full lines in No. 2, Fig. 196, keeping the axial line