y=-senx-cosx

y=-(senx+cosx)

y=-sqrt(2){[(sqrt(2).senx)/2]+[(sqrt(2).cosx)/2]}

y=-sqrt(2).sen(45+x)

you will have a function that ranges from -sqrt(2) to sqrt(2);translated to the left by 45 degrees and being the reflex of the function y=sqrt(2).sen(45+x)

hope it helps

=)