平方根の値の計算

平叙文(数学)と命令文(プログラム)の確認問題
じょじょに値を近づけていく方法で平方根の値を算出している

 (defun abs (x) (cond ((> x 0) x)

		     ((= x 0) 0) 

		     ((< x 0) (- x))))

 abs
 (defun average (x y)

   (/ (+ x y) 2))

 average
 (defun improve (guess x)

   (average guess (/ x guess)))

 improve
 (defun square (x) (* x x))

 square 
 (defun good-enough? (guess x)

   (< (abs (- (square guess) x)) 0.001))

 good-enough?
 (defun sqrt-iter (guess x)

   (if (good-enough? guess x)

       guess

     (sqrt-iter (improve guess x) x)))

 sqrt-iter
 (sqrt-iter 1 2)

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