Inquiry about Symbolics.jl

I am running Julia 1.6.7 on a Linux machine and
trying to use the Symbolics.jl package.

Any assistance with the following would be appreciated.

(1) The function simplify() does not simplify the
following trigonometric expression to -1. How can this
simplification be achieved?

julia> y = -(sin(x1t))^2 - (cos(x1t))^2
-(cos(x1(t))^2) - (sin(x1(t))^2)

julia> Symbolics.simplify(y)
-(cos(x1(t))^2) - (sin(x1(t))^2)

(2) The function expand() does not seem to expand
trigonometric functions. Is there a way to achieve
such expansions?

julia> Symbolics.expand(sin(x1t+x2t))
sin(x1(t) + x2(t))

julia> Symbolics.expand(cos(x1t+x2t))
cos(x1(t) + x2(t))

(3) How can irrational values, eg. sqrt(2), exp(1),
etc, be represented and manipulated exactly in