已知函数f(x)=x-√x2-2 的定义域为(√2,正无穷),求值域和证明在(√2,正无穷)内是减函函数f(x)=x-√x2-2 的定义域为(√2,正无穷)x>√2√x2-2>0x+√x2-2>√21/(x+√x2-2)0√x1^2-2+√x2^2-2>0(x1+x2)/(√x1^2-2+√x2^2... 已知函数f(x)=x-√x2-2 的定义域为(√2,正无穷),求值域和证明在(√2,正无穷)内是减函函数f(x)=x-√x2-2 的定义域为(√2,正无穷)x>√2√x2-2>0x+√x2-2>√21/(x+√x2-2)0√x1^2-2+√x2^2-2>0(x1+x2)/(√x1^2-2+√x2^2...