I have two equations that are valid under the substitution sin <-> cos, so a simple way to generate the second equation is to replace all occurrences of sin with cos. But Maple gets the wrong answer when I do this, because of its built-in simplification. Here is an example. Z1 and Y1 shows the problem; Z2 and Y2 shows that my attempt to overcome the problem doesn't work. Z3 doesn't work either, proving that the problem is internally generated by Maple because Maple insists on ordering variables in its own way, no matter how I write them.

________simplified example from Maple 15

restart;

Z1:=sin(-a*x+b);

Z2:='sin(-a*x+b)';

Z3:=sin(b-a*x);

-sin(a x - b)

sin(-a x + b)

-sin(a x - b)

Y1:=subs(sin=cos,Z1);

Y2:=subs(sin=cos,Z2);

-cos(a x - b)

-cos(a x - b)

correct answer should be cos(-a*x+b) but the calculated results are off by a minus sign.

Ans1:=evalf(subs(a=1,b=2,x=3,[Y1,Y2,cos(-a*x+b)]));

[-0.5403023059, -0.5403023059, 0.5403023059]

Question: How do I override Maple's desire to stick the "-" sign outside the sin function?