Are x and y and z symbolic at the time you call solve? Or are y and z numeric?
If they are symbolic and you later substitute in numeric y and z to the solve() response get a numeric x, and then substitute the numeric x, y, and z into the cos (x) * sin (y) * cos (z) + sin (Z) formula, then you could get something other than 1 due to round-off error.
Also, if your y and z are square matrices of numeric values, then cos (x) * sin (y) * cos (z) would succeed but what not be what you want: you would need to evaluate
cos(x) .* sin(y) .* cos(z)
Notice the ".*" instead of "*" if you are working with vectors or matrices.
