Apply review comments for tests

Author: rhannequin

test/bigdecimal/test_bigmath.rb

@@ -57,10 +57,11 @@ def test_tan
     assert_in_delta(0.0, tan(BigDecimal("0.0"), N))
     assert_in_delta(0.0, tan(PI(N), N))
     assert_in_delta(1.0, tan(PI(N) / 4, N))
-    assert_in_delta(Math.sqrt(3.0), tan(PI(N) / 3, N))
+    assert_in_delta(sqrt(BigDecimal(3), N), tan(PI(N) / 3, N))
+    assert_in_delta(sqrt(BigDecimal(3), 10 * N), tan(PI(10 * N) / 3, 10 * N))
     assert_in_delta(0.0, tan(-PI(N), N))
     assert_in_delta(-1.0, tan(-PI(N) / 4, N))
-    assert_in_delta(-Math.sqrt(3.0), tan(-PI(N) / 3, N))
+    assert_in_delta(-sqrt(BigDecimal(3), N), tan(-PI(N) / 3, N))
   end
 
   def test_atan