fixes #958 (#1040)

Author: martin-henz

xml/chapter1/section1/subsection7.xml

@@ -708,23 +708,21 @@ function sqrt_iter(guess, x) {
         <REQUIRES>sqrt</REQUIRES>
         <REQUIRES>improve</REQUIRES>
         <REQUIRES>sqrt_iter</REQUIRES>	
+        <REQUIRES>square_definition</REQUIRES>	
 	<EXAMPLE>example_1.8</EXAMPLE>
 	<JAVASCRIPT>
-const error_threshold = 0.01;
+const relative_tolerance = 0.0001;
 function is_good_enough(guess, x) {
-    return relative_error(guess, improve(guess, x))
-           &lt; error_threshold;
-}
-function relative_error(estimate, reference) {
-    return abs(estimate - reference) / reference;
+    return abs(square(guess) - x) &lt; guess * relative_tolerance;
 }
 	</JAVASCRIPT>
       </SNIPPET>
     </SOLUTION>
     <SNIPPET HIDE="yes">
       <NAME>example_1.8</NAME>
       <JAVASCRIPT>
-sqrt(3);
+display(sqrt(0.0001));
+display(sqrt(4000000000000));
       </JAVASCRIPT>
       <SCHEME>
       </SCHEME>