did you mean [tex]cosx+sinx=0[/tex] ?
[tex]\mbox{for the above to be true},\\ cosx=-sinx \\ \Rightarrow cotx=-1[/tex] (or [tex]sinx=0[/tex] but this does not hold for that.)
Please only post calculus questions in this forum.
LOL,this may well be calculus...
[tex]Max(sinx+cosx)= \sqrt{2}[/tex]
[tex]Min(sinx+cosx)= -\sqrt{2}[/tex]
Since they function is continuous, it must have x such that f(x)=0