Make tan depend only on sin

rhannequin · mrkn · commit 46dca76ccc6d · 2024-09-09T13:47:18.000+09:00
diff --git a/lib/bigdecimal/math.rb b/lib/bigdecimal/math.rb
@@ -148,7 +148,9 @@ def cos(x, prec)
   #   #=> "0.999999999999999999999955588155008544487055622030633191403625599381672572e0"
   #
   def tan(x, prec)
-    sin(x, prec) / cos(x, prec)
+    sine = sin(x, prec)
+    cosine = sqrt(1 - sine**2, prec)
+    sine / cosine
   end
 
   # call-seq:
