minor tweak to an example

svn: r16543

collects/scribblings/reference/numbers.scrbl

@@ -1,6 +1,7 @@
 #lang scribble/doc
 @(require "mz.ss"
-          scheme/math)
+          scheme/math
+          (for-label scheme/math))
 
 @(define math-eval (make-base-eval))
 @(interaction-eval #:eval math-eval (require scheme/math))
@@ -508,7 +509,9 @@ produces @scheme[+nan.0] in the case that neither @scheme[y] nor
 @defproc[(make-polar [magnitude real?] [angle real?]) number?]{ Returns
  @scheme[(+ (* magnitude (cos angle)) (* magnitude (sin angle) 0+1i))].
 
-@mz-examples[(make-polar 2 3.14159)]}
+@mz-examples[#:eval math-eval
+                    (make-polar 10 (* pi 1/2))
+                    (make-polar 10 (* pi 1/4))]}
 
 
 @defproc[(real-part [z number?]) real?]{ Returns the real part of