@Adri van der Meer 

thanks very much this is my best answer 

this rule "eval" is the best and i am search for it thanks

good wishes

@Carl Love   and can you Explanation this implicitdiff({x=cos(t), y=sin(t)}, {y,t}, y, x, x);  i don't know but

i know this implicitdiff({x=cos(t), y=sin(t)}, {y,t}, y, x);

(-cos(t)/sin(t))' = (cos(t)^2+sin(t)^2)/sin(t)^2 

thanks

@Carl Love   and  thanks you very much for your best answer and time to read this question

@gkokovidis  thanks for your answer and time to read this question