Comparing this equation with ux 2 +vy 2 +w2 2 +22G'y2+2v'zx+2W'xy=0, we obtain as the condition for the general equation of the second degree to represent a circle :- (v+w-2u')Ia 2 = (w +u -2v')/b2 = (u+v-2w')lc2 In tangential q, r) co-ordinates the inscribed circle has for its equation(s - a)qr+ (s - b)rp+ (s - c) pq = o, s being equal to 1(a +b +c); an alternative form is qr cot zA+rp cot ZB +pq cot2C =o; Tangential the centre is ap+bq+cr = o, or sinA +q sin B+rsinC =o.
+(s - b)pq= oor - qr cot 2A+rptan ZB +pgtan 2C=o,with centre - ap+bq+cr = o.
Exact formulae are: - Area = 2a 2 (0 - sin 0)=1a 2 0 - 4c2 cot zB =Za 2 -2 c?1 (a 2 -4c 2).
20 and 30 (mb) had special names; 40-90 were named as if plurals of the units 4-9, as in Semitic. 100, fat; 1000, ~,; 10,000, zb; 100,000, lifnw.