f(x)定义域为R,0∈R定义域中有0,
要使f(x)为奇函数,则须对x∈R,f(-x)=-f(x),
必有f(-0)=-f(0),即f(0)=-f(0),2f(0)=0,f(0)=0,
而f(0)=2^(-0)-(2^0)lga=1-lga=0,lga=1=lg10,即实数a=10