Merge pull request #414 from ErikQQY/master

Fix TRIG_EXP_RULES

Author: shashi

src/simplify_rules.jl

@@ -60,8 +60,8 @@ let
         @acrule(~r*~x::has_trig_exp + ~r*~y => ~r*(~x + ~y))
         @acrule(~r*~x::has_trig_exp + -1*~r*~y => ~r*(~x - ~y))
         @acrule(sin(~x)^2 + cos(~x)^2 => one(~x))
-        @acrule(sin(~x)^2 + -1        => cos(~x)^2)
-        @acrule(cos(~x)^2 + -1        => sin(~x)^2)
+        @acrule(sin(~x)^2 + -1        => -1*cos(~x)^2)
+        @acrule(cos(~x)^2 + -1        => -1*sin(~x)^2)
 
         @acrule(cos(~x)^2 + -1*sin(~x)^2 => cos(2 * ~x))
         @acrule(sin(~x)^2 + -1*cos(~x)^2 => -cos(2 * ~x))

test/rulesets.jl

@@ -86,6 +86,8 @@ end
 
     @eqtest simplify(1 + y + tan(x)^2) == sec(x)^2 + y
     @eqtest simplify(1 + y + cot(x)^2) == csc(x)^2 + y
+    @eqtest simplify(cos(x)^2 - 1) == -sin(x)^2
+    @eqtest simplify(sin(x)^2 - 1) == -cos(x)^2
 end
 
 @testset "Double angle formulas" begin