!! sqrt の近似
ルート（√）の近似
*https://www.mirai-kougaku.jp/laboratory/pages/240913.php

! √2 の近似
x(n+1)=(xn/2)+(1/xn)
 x(0) = 1 から
 x(1) = (1/2)+(1/1)
 x(2) = (3/4)+)(1/3)
 x(3) = (17/24)+(12/17)
 x(4) = (577/816)+(408/577)

 ( x(0) = 3 からも計算可能 )

! √3
x(n+1) = (xn/2)+(3/(2*xn))

! √5
x(n+1) = (xn/2)+(5/(2*xn))