15. 已知f(x)f(x)f(x)为奇函数,g(x)g(x)g(x)为偶函数,且满足f(x)+g(x)=ex+xf(x)+g(x)=e^{x}+xf(x)+g(x)=ex+x,则g(x)=(g(x)=(g(x)=( )))