20．已知函数f(x)=ex−e−x2f(x)=\frac{{e}^{x}-{e}^{-x}}{2}f(x)=2ex−e−x，g(x)=ex+e−x2g(x)=\frac{{e}^{x}+{e}^{-x}}{2}g(x)=2ex+e−x，则f(x)f(x)f(x)，g(x)g(x)g(x)满足((( )))