[ 576 ] 
Sec. where the fadtor 4 a z takes place inftead of w* 
-j- fq. of the tang, of c?o°. 
2 n 
If y be = — 1, and n an even number, a-p a + 
n n zn . _ 
2 xa-f~co xa — oo -f -a — co is = 4 x oo 2 J~ b % x 
Sec. 
Whence, by extracting the fquare root of both 
fides of thofe equations, we have, when n is an odd 
n n 
number, a + co a — co = 2 a n x V oo z ~p b* x 
V w J -(- c *, &c. 2 a taking place inftead of 
V of -f- fq. of the tang, of (jo° : And, when n is an 
n n 
even number, a~p co + a — co =2 x V co z b* x 
V' 'f- c z 3 Sec. Hence we infer this conftrudtion. 
XIII. 
Having describ'd about the centre C (Jig. 3. and 
4.), with the radius a , the circle P a' A a" A\ See. 
draw the diameter P C Q, and the tangent b" P b 4 ; 
divide the femicircumterence Pa ' Q into as many 
equal parts P a, a A, A a'\ Sec. as there are units in 
2 n ; draw the fecants C a b\ C a" b\ Sec. and, thro’ 
any point ( 0 ) in draw k" 0 P parallel to b" P P j 
likewife draw b' k\ b" k". Sec. parallel to P and 
call C O, co. 
Then, if the radius be i, p will be the cofine of 
twice the angfe P C q the cofine of twice P C a ", 
Sec. therefore P b' — 0 k' will b e = b, P b' = 0 k' < 
= c , Sec. and C U = V co % + P, C k ' = V w * -j- c\ 
See. 
Con- 
