f(x1+x2)=2^(x1+x2),f(x1)*f(x2)=2^x1*2^x2=2^(x1+x2),所以①满足;
f(x1*x2)=2^(x1*x2),这不等于f(x1)+f(x2)的值,所以②不满足;
当x1>x2时,f(x1)-f(x2)>0,x1-x2>0,[f(x1)-f(x2)]*(x1-x2)>0.
当x1
f(x1+x2)=2^(x1+x2),f(x1)*f(x2)=2^x1*2^x2=2^(x1+x2),所以①满足;
f(x1*x2)=2^(x1*x2),这不等于f(x1)+f(x2)的值,所以②不满足;
当x1>x2时,f(x1)-f(x2)>0,x1-x2>0,[f(x1)-f(x2)]*(x1-x2)>0.
当x1