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PYRAMIDAL SYSTEM. 27 faces of 100 truncate the solid angles in which the edges k, l meet; and the faces of lio truncate the edges l. Ml,001 = 90°— |l ; cos (hid,loo) = cos45°cos |l ; Ml, ioo = Jl. 98. In the form Mil (fig. 37), W = 180°— L, T = 180°— K. FIG. 37. FIG. 38. 99. In combinations of the form Mil with the forms 001, 100, 110, the faces of 001 truncate the edges w; the faces of 100 truncate the edges t ; and the aces of 110 truncate the solid angles in which the edges t, w meet. 100. Let p, q be two adjacent poles of one of the forms Ml, P 0r , equidistant from 0 the pole of 001; and let the arc pq contain s, a pole of the other form. Then, tansc = cos45°tanPC. ^ le ^ orm hkl (fig. 38) has sixteen tan^> = ^ tanin = |cotE cos<j>, sin^K = cos^Lsin^, sin|F = cos ^l cos (46°+ <f). 102. In combinations of the form Ml with the forms 001, 100, 110, the faces of 001 truncate the solid angles in which the edges k, F meet; the laces of 100 truncate the solid angles in which the edges k, l meet; and the faces of 110 truncate the solid angles in which the edges f, l meet. 7iI7,ooi = eo°— |l; cos(7(17,100) = cos^l cos<f> ; cos (7(7.7,110) = cos |l sin (46°-f <p). 103. In the form kMI (fig. 39), sin |g = cos sin (45°+ <f), cosIt = cosJlcob^. c °mhinations of the form kMI with the form 100, the faces of 100 truncate the edges t. fig. 39,